diff --git a/docs/testsuite b/docs/testsuite
index ec87429c..ea706649 100644
--- a/docs/testsuite
+++ b/docs/testsuite
@@ -36,8 +36,8 @@ that, but it will also be useful for every future change.
 
 Apart from this document, you should also have a look at:
 
-1. The "Modern Perl" book, which can be found at
-   http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+1. The "Modern Perl" book:
+   https://i3wm.org/downloads/modern_perl_a4.pdf
 2. The latest Perl documentation of the "i3test" (general testcase setup) and
    "i3test::Test" (additional test instructions) modules:
    https://build.i3wm.org/docs/lib-i3test.html respectively
diff --git a/testcases/new-test b/testcases/new-test
index e0b2e13f..57e50341 100755
--- a/testcases/new-test
+++ b/testcases/new-test
@@ -53,7 +53,7 @@ my $header = <<'EOF';
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # TODO: Description of this file.
diff --git a/testcases/t/001-tile.t b/testcases/t/001-tile.t
index 356b7b3a..c6bf7b24 100644
--- a/testcases/t/001-tile.t
+++ b/testcases/t/001-tile.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test;
diff --git a/testcases/t/002-i3-sync.t b/testcases/t/002-i3-sync.t
index 9466f860..4b108405 100644
--- a/testcases/t/002-i3-sync.t
+++ b/testcases/t/002-i3-sync.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # checks if i3 supports I3_SYNC
diff --git a/testcases/t/003-ipc.t b/testcases/t/003-ipc.t
index 89c60f1c..94c2c56e 100644
--- a/testcases/t/003-ipc.t
+++ b/testcases/t/003-ipc.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test;
diff --git a/testcases/t/004-unmanaged.t b/testcases/t/004-unmanaged.t
index 1f3c6ccd..88cdc522 100644
--- a/testcases/t/004-unmanaged.t
+++ b/testcases/t/004-unmanaged.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test;
diff --git a/testcases/t/005-floating.t b/testcases/t/005-floating.t
index d85826b3..61c26cba 100644
--- a/testcases/t/005-floating.t
+++ b/testcases/t/005-floating.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test;
diff --git a/testcases/t/100-fullscreen.t b/testcases/t/100-fullscreen.t
index a14cb8ba..26ec9fe6 100644
--- a/testcases/t/100-fullscreen.t
+++ b/testcases/t/100-fullscreen.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test;
diff --git a/testcases/t/101-focus.t b/testcases/t/101-focus.t
index 1e87a544..0784979b 100644
--- a/testcases/t/101-focus.t
+++ b/testcases/t/101-focus.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test;
diff --git a/testcases/t/102-dock.t b/testcases/t/102-dock.t
index 60352d6d..1b513cb4 100644
--- a/testcases/t/102-dock.t
+++ b/testcases/t/102-dock.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test;
diff --git a/testcases/t/104-focus-stack.t b/testcases/t/104-focus-stack.t
index d2193368..7624a13e 100644
--- a/testcases/t/104-focus-stack.t
+++ b/testcases/t/104-focus-stack.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Checks if the focus is correctly restored, when creating a floating client
diff --git a/testcases/t/111-goto.t b/testcases/t/111-goto.t
index ade653d1..8617be47 100644
--- a/testcases/t/111-goto.t
+++ b/testcases/t/111-goto.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test;
diff --git a/testcases/t/112-floating-resize.t b/testcases/t/112-floating-resize.t
index 947ca3b6..d393cac1 100644
--- a/testcases/t/112-floating-resize.t
+++ b/testcases/t/112-floating-resize.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test;
diff --git a/testcases/t/113-urgent.t b/testcases/t/113-urgent.t
index 0de90193..f78226e3 100644
--- a/testcases/t/113-urgent.t
+++ b/testcases/t/113-urgent.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test i3_autostart => 0;
diff --git a/testcases/t/114-client-leader.t b/testcases/t/114-client-leader.t
index 3ecc644d..7826f028 100644
--- a/testcases/t/114-client-leader.t
+++ b/testcases/t/114-client-leader.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test;
diff --git a/testcases/t/115-ipc-workspaces.t b/testcases/t/115-ipc-workspaces.t
index b0c4354e..d47e525c 100644
--- a/testcases/t/115-ipc-workspaces.t
+++ b/testcases/t/115-ipc-workspaces.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test;
diff --git a/testcases/t/116-nestedcons.t b/testcases/t/116-nestedcons.t
index 7b15c5f0..a945b034 100644
--- a/testcases/t/116-nestedcons.t
+++ b/testcases/t/116-nestedcons.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test;
diff --git a/testcases/t/117-workspace.t b/testcases/t/117-workspace.t
index 6345ae68..f9283a6f 100644
--- a/testcases/t/117-workspace.t
+++ b/testcases/t/117-workspace.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests whether we can switch to a non-existent workspace
diff --git a/testcases/t/118-openkill.t b/testcases/t/118-openkill.t
index 08b5cda9..ad82c18b 100644
--- a/testcases/t/118-openkill.t
+++ b/testcases/t/118-openkill.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests whether opening an empty container and killing it again works
diff --git a/testcases/t/119-match.t b/testcases/t/119-match.t
index 65c41f1f..33a8d580 100644
--- a/testcases/t/119-match.t
+++ b/testcases/t/119-match.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests all kinds of matching methods
diff --git a/testcases/t/120-multiple-cmds.t b/testcases/t/120-multiple-cmds.t
index 114d7129..7d3a5fb6 100644
--- a/testcases/t/120-multiple-cmds.t
+++ b/testcases/t/120-multiple-cmds.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests multiple commands (using ';') and multiple operations (using ',')
diff --git a/testcases/t/121-next-prev.t b/testcases/t/121-next-prev.t
index 72c52c9a..758ab10a 100644
--- a/testcases/t/121-next-prev.t
+++ b/testcases/t/121-next-prev.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests focus switching (next/prev)
diff --git a/testcases/t/122-split.t b/testcases/t/122-split.t
index fe93880c..66f26ce6 100644
--- a/testcases/t/122-split.t
+++ b/testcases/t/122-split.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests splitting
diff --git a/testcases/t/124-move.t b/testcases/t/124-move.t
index b4a8ca3e..27d56ef4 100644
--- a/testcases/t/124-move.t
+++ b/testcases/t/124-move.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests moving. Basically, there are four different code-paths:
diff --git a/testcases/t/126-regress-close.t b/testcases/t/126-regress-close.t
index bdb31df2..3e02602c 100644
--- a/testcases/t/126-regress-close.t
+++ b/testcases/t/126-regress-close.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression: closing of floating clients did crash i3 when closing the
diff --git a/testcases/t/127-regress-floating-parent.t b/testcases/t/127-regress-floating-parent.t
index ebacd3e5..3571fb85 100644
--- a/testcases/t/127-regress-floating-parent.t
+++ b/testcases/t/127-regress-floating-parent.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression: make a container floating, kill its parent, make it tiling again
diff --git a/testcases/t/128-open-order.t b/testcases/t/128-open-order.t
index b0ab321f..1e52d77b 100644
--- a/testcases/t/128-open-order.t
+++ b/testcases/t/128-open-order.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Check if new containers are opened after the currently focused one instead
diff --git a/testcases/t/129-focus-after-close.t b/testcases/t/129-focus-after-close.t
index 8bfa0140..fe498b9c 100644
--- a/testcases/t/129-focus-after-close.t
+++ b/testcases/t/129-focus-after-close.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Check if the focus is correctly restored after closing windows.
diff --git a/testcases/t/130-close-empty-split.t b/testcases/t/130-close-empty-split.t
index 2e3cb794..62b49ed5 100644
--- a/testcases/t/130-close-empty-split.t
+++ b/testcases/t/130-close-empty-split.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Check if empty split containers are automatically closed.
diff --git a/testcases/t/131-stacking-order.t b/testcases/t/131-stacking-order.t
index 3d89e0f3..7e0c7768 100644
--- a/testcases/t/131-stacking-order.t
+++ b/testcases/t/131-stacking-order.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Check if stacking containers can be used independently of
diff --git a/testcases/t/132-move-workspace.t b/testcases/t/132-move-workspace.t
index c7721c3d..bcfdaa7e 100644
--- a/testcases/t/132-move-workspace.t
+++ b/testcases/t/132-move-workspace.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Checks if the 'move [window/container] to workspace' command works correctly
diff --git a/testcases/t/133-size-hints.t b/testcases/t/133-size-hints.t
index a16c5399..c7e8e889 100644
--- a/testcases/t/133-size-hints.t
+++ b/testcases/t/133-size-hints.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Checks if size hints are interpreted correctly.
diff --git a/testcases/t/134-invalid-command.t b/testcases/t/134-invalid-command.t
index c10771c8..ed4cad00 100644
--- a/testcases/t/134-invalid-command.t
+++ b/testcases/t/134-invalid-command.t
@@ -12,7 +12,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 #
diff --git a/testcases/t/135-floating-focus.t b/testcases/t/135-floating-focus.t
index 168151f4..3666add9 100644
--- a/testcases/t/135-floating-focus.t
+++ b/testcases/t/135-floating-focus.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test;
diff --git a/testcases/t/136-floating-ws-empty.t b/testcases/t/136-floating-ws-empty.t
index 6b2a028e..7bc739e5 100644
--- a/testcases/t/136-floating-ws-empty.t
+++ b/testcases/t/136-floating-ws-empty.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test: when only having a floating window on a workspace, it should
diff --git a/testcases/t/137-floating-unmap.t b/testcases/t/137-floating-unmap.t
index 97aa02e0..261b4a09 100644
--- a/testcases/t/137-floating-unmap.t
+++ b/testcases/t/137-floating-unmap.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test: Floating windows were not correctly unmapped when switching
diff --git a/testcases/t/138-floating-attach.t b/testcases/t/138-floating-attach.t
index fecb3cb3..f24026fa 100644
--- a/testcases/t/138-floating-attach.t
+++ b/testcases/t/138-floating-attach.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test: New windows were attached to the container of a floating window
diff --git a/testcases/t/139-ws-numbers.t b/testcases/t/139-ws-numbers.t
index 5d808c0b..4817b396 100644
--- a/testcases/t/139-ws-numbers.t
+++ b/testcases/t/139-ws-numbers.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Check if numbered workspaces and named workspaces are sorted in the right way
diff --git a/testcases/t/140-focus-lost.t b/testcases/t/140-focus-lost.t
index c13cfdc4..dca67d54 100644
--- a/testcases/t/140-focus-lost.t
+++ b/testcases/t/140-focus-lost.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression: Check if the focus stays the same when switching the layout
diff --git a/testcases/t/141-resize.t b/testcases/t/141-resize.t
index 5a264169..78e25956 100644
--- a/testcases/t/141-resize.t
+++ b/testcases/t/141-resize.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests resizing tiling containers
diff --git a/testcases/t/142-regress-move-floating.t b/testcases/t/142-regress-move-floating.t
index f1ff051e..2aa8c6c0 100644
--- a/testcases/t/142-regress-move-floating.t
+++ b/testcases/t/142-regress-move-floating.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression: move a floating window to a different workspace crashes i3
diff --git a/testcases/t/143-regress-floating-restart.t b/testcases/t/143-regress-floating-restart.t
index 816793c6..8f6ab6f0 100644
--- a/testcases/t/143-regress-floating-restart.t
+++ b/testcases/t/143-regress-floating-restart.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression: floating windows are tiling after restarting, closing them crashes i3
diff --git a/testcases/t/144-regress-floating-resize.t b/testcases/t/144-regress-floating-resize.t
index d21e8289..50683165 100644
--- a/testcases/t/144-regress-floating-resize.t
+++ b/testcases/t/144-regress-floating-resize.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression: when resizing two containers on a workspace, opening a floating
diff --git a/testcases/t/145-flattening.t b/testcases/t/145-flattening.t
index 3f84cdc1..b5f6b62d 100644
--- a/testcases/t/145-flattening.t
+++ b/testcases/t/145-flattening.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # by moving the window in the opposite orientation that its parent has, we
diff --git a/testcases/t/146-floating-reinsert.t b/testcases/t/146-floating-reinsert.t
index 0742a037..49f39551 100644
--- a/testcases/t/146-floating-reinsert.t
+++ b/testcases/t/146-floating-reinsert.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 use i3test;
diff --git a/testcases/t/147-regress-floatingmove.t b/testcases/t/147-regress-floatingmove.t
index a03b87d7..60205ea4 100644
--- a/testcases/t/147-regress-floatingmove.t
+++ b/testcases/t/147-regress-floatingmove.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test for moving a con outside of a floating con when there are no
diff --git a/testcases/t/148-regress-floatingmovews.t b/testcases/t/148-regress-floatingmovews.t
index 2bee4249..329d2559 100644
--- a/testcases/t/148-regress-floatingmovews.t
+++ b/testcases/t/148-regress-floatingmovews.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test for correct focus behaviour when moving a floating con to
diff --git a/testcases/t/150-regress-dock-restart.t b/testcases/t/150-regress-dock-restart.t
index 0fb15a56..d849d195 100644
--- a/testcases/t/150-regress-dock-restart.t
+++ b/testcases/t/150-regress-dock-restart.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test for inplace restarting with dock clients
diff --git a/testcases/t/151-regress-float-size.t b/testcases/t/151-regress-float-size.t
index c6069d81..1aae00cd 100644
--- a/testcases/t/151-regress-float-size.t
+++ b/testcases/t/151-regress-float-size.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test for setting a window to floating, tiling and opening a new window
diff --git a/testcases/t/152-regress-level-up.t b/testcases/t/152-regress-level-up.t
index ba6820a3..b06ab46d 100644
--- a/testcases/t/152-regress-level-up.t
+++ b/testcases/t/152-regress-level-up.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test for using level-up to get to the 'content'-container and
diff --git a/testcases/t/153-floating-originalsize.t b/testcases/t/153-floating-originalsize.t
index 87e7e531..dafa853f 100644
--- a/testcases/t/153-floating-originalsize.t
+++ b/testcases/t/153-floating-originalsize.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test if the requested width/height is set after making the window floating.
diff --git a/testcases/t/154-regress-multiple-dock.t b/testcases/t/154-regress-multiple-dock.t
index 5ae84f06..bf841ef1 100644
--- a/testcases/t/154-regress-multiple-dock.t
+++ b/testcases/t/154-regress-multiple-dock.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test for closing one of multiple dock clients
diff --git a/testcases/t/155-floating-split-size.t b/testcases/t/155-floating-split-size.t
index 4f9b12f3..5221f585 100644
--- a/testcases/t/155-floating-split-size.t
+++ b/testcases/t/155-floating-split-size.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test to see if i3 combines the geometry of all children in a split container
diff --git a/testcases/t/156-fullscreen-focus.t b/testcases/t/156-fullscreen-focus.t
index 62711915..3af158aa 100644
--- a/testcases/t/156-fullscreen-focus.t
+++ b/testcases/t/156-fullscreen-focus.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test if new containers get focused when there is a fullscreen container at
diff --git a/testcases/t/158-wm_take_focus.t b/testcases/t/158-wm_take_focus.t
index c4b42964..e9a32cd0 100644
--- a/testcases/t/158-wm_take_focus.t
+++ b/testcases/t/158-wm_take_focus.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests if the WM_TAKE_FOCUS protocol is correctly handled by i3
diff --git a/testcases/t/159-socketpaths.t b/testcases/t/159-socketpaths.t
index e73239ad..072d6940 100644
--- a/testcases/t/159-socketpaths.t
+++ b/testcases/t/159-socketpaths.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests if the various ipc_socket_path options are correctly handled
diff --git a/testcases/t/161-regress-borders-restart.t b/testcases/t/161-regress-borders-restart.t
index 0b45df06..31cf9398 100644
--- a/testcases/t/161-regress-borders-restart.t
+++ b/testcases/t/161-regress-borders-restart.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test to check if borders are correctly restored after an inplace
diff --git a/testcases/t/162-regress-dock-urgent.t b/testcases/t/162-regress-dock-urgent.t
index d558b0d9..36a5625a 100644
--- a/testcases/t/162-regress-dock-urgent.t
+++ b/testcases/t/162-regress-dock-urgent.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test for setting the urgent hint on dock clients.
diff --git a/testcases/t/163-wm-state.t b/testcases/t/163-wm-state.t
index 8b679386..7e165558 100644
--- a/testcases/t/163-wm-state.t
+++ b/testcases/t/163-wm-state.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests if WM_STATE is WM_STATE_NORMAL when mapped and WM_STATE_WITHDRAWN when
diff --git a/testcases/t/164-kill-win-vs-client.t b/testcases/t/164-kill-win-vs-client.t
index fe3fd011..d48301d8 100644
--- a/testcases/t/164-kill-win-vs-client.t
+++ b/testcases/t/164-kill-win-vs-client.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests if WM_STATE is WM_STATE_NORMAL when mapped and WM_STATE_WITHDRAWN when
diff --git a/testcases/t/165-for_window.t b/testcases/t/165-for_window.t
index 5ea5183c..77fbf848 100644
--- a/testcases/t/165-for_window.t
+++ b/testcases/t/165-for_window.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 use i3test i3_autostart => 0;
diff --git a/testcases/t/166-assign.t b/testcases/t/166-assign.t
index 249bbf87..bb817b6c 100644
--- a/testcases/t/166-assign.t
+++ b/testcases/t/166-assign.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests if assignments work
diff --git a/testcases/t/167-workspace_layout.t b/testcases/t/167-workspace_layout.t
index 597d545e..22f6d7ca 100644
--- a/testcases/t/167-workspace_layout.t
+++ b/testcases/t/167-workspace_layout.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests the workspace_layout config option.
diff --git a/testcases/t/168-regress-fullscreen-restart.t b/testcases/t/168-regress-fullscreen-restart.t
index 421c1abc..2f012cb6 100644
--- a/testcases/t/168-regress-fullscreen-restart.t
+++ b/testcases/t/168-regress-fullscreen-restart.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that i3 survives inplace restarts with fullscreen containers
diff --git a/testcases/t/169-border-toggle.t b/testcases/t/169-border-toggle.t
index 4146fd79..cc94bf2a 100644
--- a/testcases/t/169-border-toggle.t
+++ b/testcases/t/169-border-toggle.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests if the 'border toggle' command works correctly
diff --git a/testcases/t/170-force_focus_wrapping.t b/testcases/t/170-force_focus_wrapping.t
index 20641b0a..718b5d98 100644
--- a/testcases/t/170-force_focus_wrapping.t
+++ b/testcases/t/170-force_focus_wrapping.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests if the 'force_focus_wrapping' config directive works correctly.
diff --git a/testcases/t/171-config-migrate.t b/testcases/t/171-config-migrate.t
index 99158eab..eb66a853 100644
--- a/testcases/t/171-config-migrate.t
+++ b/testcases/t/171-config-migrate.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests if i3-migrate-config-to-v4 correctly migrates all config file
diff --git a/testcases/t/172-start-on-named-ws.t b/testcases/t/172-start-on-named-ws.t
index d1af6c07..a5b64fd9 100644
--- a/testcases/t/172-start-on-named-ws.t
+++ b/testcases/t/172-start-on-named-ws.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # checks if i3 starts up on workspace '1' or the first configured named workspace
diff --git a/testcases/t/173-get-marks.t b/testcases/t/173-get-marks.t
index 556014a1..01169704 100644
--- a/testcases/t/173-get-marks.t
+++ b/testcases/t/173-get-marks.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # checks if the IPC message type get_marks works correctly
diff --git a/testcases/t/174-border-config.t b/testcases/t/174-border-config.t
index 66e2cb65..94c06fe6 100644
--- a/testcases/t/174-border-config.t
+++ b/testcases/t/174-border-config.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests the new_window and new_float config option.
diff --git a/testcases/t/175-startup-notification.t b/testcases/t/175-startup-notification.t
index cd6f3950..a5f3ba5b 100644
--- a/testcases/t/175-startup-notification.t
+++ b/testcases/t/175-startup-notification.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test for the startup notification protocol.
diff --git a/testcases/t/176-workspace-baf.t b/testcases/t/176-workspace-baf.t
index 16738429..fa329f19 100644
--- a/testcases/t/176-workspace-baf.t
+++ b/testcases/t/176-workspace-baf.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Checks if the 'workspace back_and_forth' command and the
diff --git a/testcases/t/177-bar-config.t b/testcases/t/177-bar-config.t
index 278fd596..1ced3ce0 100644
--- a/testcases/t/177-bar-config.t
+++ b/testcases/t/177-bar-config.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Checks that the bar config is parsed correctly.
diff --git a/testcases/t/178-regress-workspace-open.t b/testcases/t/178-regress-workspace-open.t
index 17bce095..f11e3734 100644
--- a/testcases/t/178-regress-workspace-open.t
+++ b/testcases/t/178-regress-workspace-open.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests if empty workspaces are closed when the last child
diff --git a/testcases/t/179-regress-multiple-ws.t b/testcases/t/179-regress-multiple-ws.t
index 7ed2b75d..21abafce 100644
--- a/testcases/t/179-regress-multiple-ws.t
+++ b/testcases/t/179-regress-multiple-ws.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # The command "move workspace prev; workspace prev" will lead to an error.
diff --git a/testcases/t/180-fd-leaks.t b/testcases/t/180-fd-leaks.t
index 6ca0dc6f..8413e571 100644
--- a/testcases/t/180-fd-leaks.t
+++ b/testcases/t/180-fd-leaks.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that i3 does not leak any file descriptors in 'exec'.
diff --git a/testcases/t/181-regress-float-border.t b/testcases/t/181-regress-float-border.t
index b6352e1c..fb019d22 100644
--- a/testcases/t/181-regress-float-border.t
+++ b/testcases/t/181-regress-float-border.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test: Changing border style should not have an impact on the size
diff --git a/testcases/t/182-regress-focus-dock.t b/testcases/t/182-regress-focus-dock.t
index 198bd2d7..a47b0ecd 100644
--- a/testcases/t/182-regress-focus-dock.t
+++ b/testcases/t/182-regress-focus-dock.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test: Focusing a dock window should just do nothing, not crash i3.
diff --git a/testcases/t/183-config-variables.t b/testcases/t/183-config-variables.t
index d135ed59..515d763d 100644
--- a/testcases/t/183-config-variables.t
+++ b/testcases/t/183-config-variables.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Checks that variables are parsed correctly by using for_window rules with
diff --git a/testcases/t/184-regress-float-split-resize.t b/testcases/t/184-regress-float-split-resize.t
index f785eb84..92b4bd5a 100644
--- a/testcases/t/184-regress-float-split-resize.t
+++ b/testcases/t/184-regress-float-split-resize.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression: resizing a floating split container leads to a crash.
diff --git a/testcases/t/185-scratchpad.t b/testcases/t/185-scratchpad.t
index 0cd9ac3b..00563785 100644
--- a/testcases/t/185-scratchpad.t
+++ b/testcases/t/185-scratchpad.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests for the scratchpad functionality.
diff --git a/testcases/t/186-regress-assign-focus-parent.t b/testcases/t/186-regress-assign-focus-parent.t
index 49d8ea75..50665f6d 100644
--- a/testcases/t/186-regress-assign-focus-parent.t
+++ b/testcases/t/186-regress-assign-focus-parent.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test: New windows were not opened in the correct place if they
diff --git a/testcases/t/187-commands-parser.t b/testcases/t/187-commands-parser.t
index c2ff4a26..5eaadd35 100644
--- a/testcases/t/187-commands-parser.t
+++ b/testcases/t/187-commands-parser.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests the standalone parser binary to see if it calls the right code when
diff --git a/testcases/t/188-regress-focus-restart.t b/testcases/t/188-regress-focus-restart.t
index 51d3a8a7..0f73feea 100644
--- a/testcases/t/188-regress-focus-restart.t
+++ b/testcases/t/188-regress-focus-restart.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that i3 survives inplace restarts with fullscreen containers
diff --git a/testcases/t/189-floating-constraints.t b/testcases/t/189-floating-constraints.t
index ba5f76aa..87e1f223 100644
--- a/testcases/t/189-floating-constraints.t
+++ b/testcases/t/189-floating-constraints.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests the floating_{minimum,maximum}_size config options.
diff --git a/testcases/t/190-scratchpad-diff-ws.t b/testcases/t/190-scratchpad-diff-ws.t
index 23327110..acbfa972 100644
--- a/testcases/t/190-scratchpad-diff-ws.t
+++ b/testcases/t/190-scratchpad-diff-ws.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test for ticket #676: 'scratchpad show' causes a segfault if the scratchpad
diff --git a/testcases/t/191-resize-levels.t b/testcases/t/191-resize-levels.t
index 9e483230..fe3561d4 100644
--- a/testcases/t/191-resize-levels.t
+++ b/testcases/t/191-resize-levels.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that you can resize across different levels of containers even when
diff --git a/testcases/t/192-layout.t b/testcases/t/192-layout.t
index c86b3656..db3dff76 100644
--- a/testcases/t/192-layout.t
+++ b/testcases/t/192-layout.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that switching between the different layouts works as expected.
diff --git a/testcases/t/193-ipc-version.t b/testcases/t/193-ipc-version.t
index 82449de7..475bf85d 100644
--- a/testcases/t/193-ipc-version.t
+++ b/testcases/t/193-ipc-version.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that we can get the version number of i3 via IPC.
diff --git a/testcases/t/194-regress-floating-size.t b/testcases/t/194-regress-floating-size.t
index 4f4217c0..61c18e7f 100644
--- a/testcases/t/194-regress-floating-size.t
+++ b/testcases/t/194-regress-floating-size.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that the size requested by floating windows is set by i3, no matter
diff --git a/testcases/t/195-net-active-window.t b/testcases/t/195-net-active-window.t
index 4ce12089..a6f0d94f 100644
--- a/testcases/t/195-net-active-window.t
+++ b/testcases/t/195-net-active-window.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that the _NET_ACTIVE_WINDOW message only changes focus when the
diff --git a/testcases/t/196-randr-output-names.t b/testcases/t/196-randr-output-names.t
index a822cdc2..caf0e67f 100644
--- a/testcases/t/196-randr-output-names.t
+++ b/testcases/t/196-randr-output-names.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verify that i3 allows strange RandR output names such as DVI-I_1/digital.
diff --git a/testcases/t/197-regression-move-vanish.t b/testcases/t/197-regression-move-vanish.t
index 7f8f9621..0c85b557 100644
--- a/testcases/t/197-regression-move-vanish.t
+++ b/testcases/t/197-regression-move-vanish.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test: moving a window to the right out of a splitv container would
diff --git a/testcases/t/198-regression-scratchpad-crash.t b/testcases/t/198-regression-scratchpad-crash.t
index c295ce3d..02229751 100644
--- a/testcases/t/198-regression-scratchpad-crash.t
+++ b/testcases/t/198-regression-scratchpad-crash.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # When using a command which moves a window to scratchpad from an invisible
diff --git a/testcases/t/199-ipc-mode-event.t b/testcases/t/199-ipc-mode-event.t
index 0e4f8960..4548fe3b 100644
--- a/testcases/t/199-ipc-mode-event.t
+++ b/testcases/t/199-ipc-mode-event.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that the IPC 'mode' event is sent when modes are changed.
diff --git a/testcases/t/200-urgency-timer.t b/testcases/t/200-urgency-timer.t
index 6d2f2bd8..4192f5b4 100644
--- a/testcases/t/200-urgency-timer.t
+++ b/testcases/t/200-urgency-timer.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 #
diff --git a/testcases/t/201-config-parser.t b/testcases/t/201-config-parser.t
index 90fc8115..c7f79093 100644
--- a/testcases/t/201-config-parser.t
+++ b/testcases/t/201-config-parser.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests the standalone parser binary to see if it calls the right code when
diff --git a/testcases/t/202-scratchpad-criteria.t b/testcases/t/202-scratchpad-criteria.t
index 9d86be94..3489d5e9 100644
--- a/testcases/t/202-scratchpad-criteria.t
+++ b/testcases/t/202-scratchpad-criteria.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that using criteria to address scratchpad windows works.
diff --git a/testcases/t/203-regress-assign-and-move.t b/testcases/t/203-regress-assign-and-move.t
index c70ce4ce..80675112 100644
--- a/testcases/t/203-regress-assign-and-move.t
+++ b/testcases/t/203-regress-assign-and-move.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that you can assign a window _and_ use for_window with a move
diff --git a/testcases/t/204-regress-scratchpad-move.t b/testcases/t/204-regress-scratchpad-move.t
index c6fd7ae5..85e57ec0 100644
--- a/testcases/t/204-regress-scratchpad-move.t
+++ b/testcases/t/204-regress-scratchpad-move.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Moves the last window of a workspace to the scratchpad. The workspace will be
diff --git a/testcases/t/205-ipc-windows.t b/testcases/t/205-ipc-windows.t
index bafd155f..798e0031 100644
--- a/testcases/t/205-ipc-windows.t
+++ b/testcases/t/205-ipc-windows.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test;
diff --git a/testcases/t/206-fullscreen-scratchpad.t b/testcases/t/206-fullscreen-scratchpad.t
index cd7c4919..1515a394 100644
--- a/testcases/t/206-fullscreen-scratchpad.t
+++ b/testcases/t/206-fullscreen-scratchpad.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 #   Assure that no window is in fullscreen mode after showing a scratchpad window
diff --git a/testcases/t/207-shmlog.t b/testcases/t/207-shmlog.t
index 94f4bdea..43f1a852 100644
--- a/testcases/t/207-shmlog.t
+++ b/testcases/t/207-shmlog.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 use i3test;
diff --git a/testcases/t/208-regress-floating-criteria.t b/testcases/t/208-regress-floating-criteria.t
index a1f264d9..3e01a215 100644
--- a/testcases/t/208-regress-floating-criteria.t
+++ b/testcases/t/208-regress-floating-criteria.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test for focus handling when using floating enable/disable with
diff --git a/testcases/t/209-ewmh-net-workarea.t b/testcases/t/209-ewmh-net-workarea.t
index 7fade619..c1583744 100644
--- a/testcases/t/209-ewmh-net-workarea.t
+++ b/testcases/t/209-ewmh-net-workarea.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies the _NET_WORKAREA hint is deleted in case it is already set on the
diff --git a/testcases/t/210-mark-unmark.t b/testcases/t/210-mark-unmark.t
index 166ca23f..3880a344 100644
--- a/testcases/t/210-mark-unmark.t
+++ b/testcases/t/210-mark-unmark.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # checks if mark and unmark work correctly
diff --git a/testcases/t/211-regress-urgency-assign.t b/testcases/t/211-regress-urgency-assign.t
index 5bcc7460..0c866bf6 100644
--- a/testcases/t/211-regress-urgency-assign.t
+++ b/testcases/t/211-regress-urgency-assign.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that windows are properly recognized as urgent when they start up
diff --git a/testcases/t/212-assign-urgency.t b/testcases/t/212-assign-urgency.t
index 2fb235d3..9536c5e2 100644
--- a/testcases/t/212-assign-urgency.t
+++ b/testcases/t/212-assign-urgency.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests if the urgency hint will be set appropriately when opening a window
diff --git a/testcases/t/213-layout-restore-simple.t b/testcases/t/213-layout-restore-simple.t
index c2c533ff..82568089 100644
--- a/testcases/t/213-layout-restore-simple.t
+++ b/testcases/t/213-layout-restore-simple.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Restores a simple layout from a JSON file.
diff --git a/testcases/t/214-layout-restore-criteria.t b/testcases/t/214-layout-restore-criteria.t
index d21ba2b2..a6d73a20 100644
--- a/testcases/t/214-layout-restore-criteria.t
+++ b/testcases/t/214-layout-restore-criteria.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests all supported criteria for the "swallows" key.
diff --git a/testcases/t/215-layout-restore-crash.t b/testcases/t/215-layout-restore-crash.t
index d9fcd54a..978c08c1 100644
--- a/testcases/t/215-layout-restore-crash.t
+++ b/testcases/t/215-layout-restore-crash.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that i3 does not crash when a layout is partially loadable.
diff --git a/testcases/t/216-layout-restore-split-swallows.t b/testcases/t/216-layout-restore-split-swallows.t
index 6baf141c..01a0e286 100644
--- a/testcases/t/216-layout-restore-split-swallows.t
+++ b/testcases/t/216-layout-restore-split-swallows.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that i3 removes swallows specifications for split containers.
diff --git a/testcases/t/217-NET_CURRENT_DESKTOP.t b/testcases/t/217-NET_CURRENT_DESKTOP.t
index 5928ec32..22b13d8c 100644
--- a/testcases/t/217-NET_CURRENT_DESKTOP.t
+++ b/testcases/t/217-NET_CURRENT_DESKTOP.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies the _NET_CURRENT_DESKTOP property correctly tracks the currently
diff --git a/testcases/t/218-regress-floating-split.t b/testcases/t/218-regress-floating-split.t
index 1c65848b..f57d1535 100644
--- a/testcases/t/218-regress-floating-split.t
+++ b/testcases/t/218-regress-floating-split.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Make sure floating containers really can't be split.
diff --git a/testcases/t/219-ipc-window-focus.t b/testcases/t/219-ipc-window-focus.t
index 770536f3..08ed7fc5 100644
--- a/testcases/t/219-ipc-window-focus.t
+++ b/testcases/t/219-ipc-window-focus.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test i3_config => <<EOT;
diff --git a/testcases/t/220-ipc-window-title.t b/testcases/t/220-ipc-window-title.t
index b5d14e23..ad5405b8 100644
--- a/testcases/t/220-ipc-window-title.t
+++ b/testcases/t/220-ipc-window-title.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test;
diff --git a/testcases/t/221-floating-type-hints.t b/testcases/t/221-floating-type-hints.t
index 0c049d8b..75c69f0e 100644
--- a/testcases/t/221-floating-type-hints.t
+++ b/testcases/t/221-floating-type-hints.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that windows with properties that indicate they should be floating
diff --git a/testcases/t/222-regress-dock-resize.t b/testcases/t/222-regress-dock-resize.t
index 272beb95..f0f606b0 100644
--- a/testcases/t/222-regress-dock-resize.t
+++ b/testcases/t/222-regress-dock-resize.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that i3 does not crash when a command is issued that would resize a dock
diff --git a/testcases/t/223-net-client-list.t b/testcases/t/223-net-client-list.t
index 83ce2989..2a755f14 100644
--- a/testcases/t/223-net-client-list.t
+++ b/testcases/t/223-net-client-list.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that _NET_CLIENT_LIST is properly updated on the root window as windows
diff --git a/testcases/t/224-regress-resize-branch.t b/testcases/t/224-regress-resize-branch.t
index aeddd877..4cf6aef2 100644
--- a/testcases/t/224-regress-resize-branch.t
+++ b/testcases/t/224-regress-resize-branch.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that i3 does not crash when resizing a split container
diff --git a/testcases/t/225-ipc-window-fullscreen.t b/testcases/t/225-ipc-window-fullscreen.t
index bc150546..a4a7ca72 100644
--- a/testcases/t/225-ipc-window-fullscreen.t
+++ b/testcases/t/225-ipc-window-fullscreen.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that the ipc window::fullscreen_mode event works properly
diff --git a/testcases/t/226-internal-workspaces.t b/testcases/t/226-internal-workspaces.t
index 054b4f40..f62624f6 100644
--- a/testcases/t/226-internal-workspaces.t
+++ b/testcases/t/226-internal-workspaces.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that internal workspaces (those whose name starts with __) cannot be
diff --git a/testcases/t/227-ipc-workspace-empty.t b/testcases/t/227-ipc-workspace-empty.t
index b1f517ef..90e04ec3 100644
--- a/testcases/t/227-ipc-workspace-empty.t
+++ b/testcases/t/227-ipc-workspace-empty.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Checks the workspace "empty" event semantics.
diff --git a/testcases/t/228-border-widths.t b/testcases/t/228-border-widths.t
index e2dc9b85..1ad9e229 100644
--- a/testcases/t/228-border-widths.t
+++ b/testcases/t/228-border-widths.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that the border widths can be set separately for floating and
diff --git a/testcases/t/229-cleanup-tmpdir.t b/testcases/t/229-cleanup-tmpdir.t
index b63de986..d611ab70 100644
--- a/testcases/t/229-cleanup-tmpdir.t
+++ b/testcases/t/229-cleanup-tmpdir.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Makes sure i3 deletes its temporary directory when exiting.
diff --git a/testcases/t/230-floating-fullscreen-restart.t b/testcases/t/230-floating-fullscreen-restart.t
index 69bc5ddb..d77eb256 100644
--- a/testcases/t/230-floating-fullscreen-restart.t
+++ b/testcases/t/230-floating-fullscreen-restart.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Ensures floating windows don’t drop out of fullscreen mode when restarting
diff --git a/testcases/t/231-ipc-floating-event.t b/testcases/t/231-ipc-floating-event.t
index 96c94a49..f054d7e3 100644
--- a/testcases/t/231-ipc-floating-event.t
+++ b/testcases/t/231-ipc-floating-event.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that the window::floating event works correctly. This event should be
diff --git a/testcases/t/232-cmd-move-criteria.t b/testcases/t/232-cmd-move-criteria.t
index 312c9660..8281ef9e 100644
--- a/testcases/t/232-cmd-move-criteria.t
+++ b/testcases/t/232-cmd-move-criteria.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that the `move [direction]` command works with criteria
diff --git a/testcases/t/233-regress-manage-focus-unmapped.t b/testcases/t/233-regress-manage-focus-unmapped.t
index 64db0bd7..6193b8fd 100644
--- a/testcases/t/233-regress-manage-focus-unmapped.t
+++ b/testcases/t/233-regress-manage-focus-unmapped.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that an assignment that unmaps a window does not disturb input focus.
diff --git a/testcases/t/234-ewmh-desktop-names.t b/testcases/t/234-ewmh-desktop-names.t
index 246a0a46..bd792902 100644
--- a/testcases/t/234-ewmh-desktop-names.t
+++ b/testcases/t/234-ewmh-desktop-names.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that the EWMH specified property _NET_DESKTOP_NAMES is updated properly
diff --git a/testcases/t/235-check-config-no-x.t b/testcases/t/235-check-config-no-x.t
index dce70894..7b7bde2d 100644
--- a/testcases/t/235-check-config-no-x.t
+++ b/testcases/t/235-check-config-no-x.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Check whether the -C option works without a display and doesn't
diff --git a/testcases/t/236-floating-focus-raise.t b/testcases/t/236-floating-focus-raise.t
index 53e5b08e..bb175bdc 100644
--- a/testcases/t/236-floating-focus-raise.t
+++ b/testcases/t/236-floating-focus-raise.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that focusing floating windows with the command `focus [direction]`
diff --git a/testcases/t/237-regress-assign-focus.t b/testcases/t/237-regress-assign-focus.t
index fa8608b8..f697558f 100644
--- a/testcases/t/237-regress-assign-focus.t
+++ b/testcases/t/237-regress-assign-focus.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that using layout tabbed followed by focus (on a window that is
diff --git a/testcases/t/238-ipc-binding-event.t b/testcases/t/238-ipc-binding-event.t
index 6916593d..403afbad 100644
--- a/testcases/t/238-ipc-binding-event.t
+++ b/testcases/t/238-ipc-binding-event.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that the binding event works properly
diff --git a/testcases/t/239-net-close-window-request.t b/testcases/t/239-net-close-window-request.t
index 763da681..73063e6f 100644
--- a/testcases/t/239-net-close-window-request.t
+++ b/testcases/t/239-net-close-window-request.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test _NET_CLOSE_WINDOW requests to close a window.
diff --git a/testcases/t/240-focus-on-window-activation.t b/testcases/t/240-focus-on-window-activation.t
index efcd5ca4..50828ff0 100644
--- a/testcases/t/240-focus-on-window-activation.t
+++ b/testcases/t/240-focus-on-window-activation.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests for the focus_on_window_activation directive
diff --git a/testcases/t/241-consistent-center.t b/testcases/t/241-consistent-center.t
index a3758554..2ea95bf4 100644
--- a/testcases/t/241-consistent-center.t
+++ b/testcases/t/241-consistent-center.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that most of i3's centering methods produce consistent results.
diff --git a/testcases/t/242-no-focus.t b/testcases/t/242-no-focus.t
index 6fd27fe0..7656d496 100644
--- a/testcases/t/242-no-focus.t
+++ b/testcases/t/242-no-focus.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test the 'no_focus' directive.
diff --git a/testcases/t/243-move-to-mark.t b/testcases/t/243-move-to-mark.t
index 390da04d..68b55135 100644
--- a/testcases/t/243-move-to-mark.t
+++ b/testcases/t/243-move-to-mark.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests for the 'move [window|container] to mark' command
diff --git a/testcases/t/244-new-workspace-floating-enable-center.t b/testcases/t/244-new-workspace-floating-enable-center.t
index 314187bd..5197fc69 100644
--- a/testcases/t/244-new-workspace-floating-enable-center.t
+++ b/testcases/t/244-new-workspace-floating-enable-center.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Ensures that 'move workspace $new, floating enable' on a marked window
diff --git a/testcases/t/245-move-position-mouse.t b/testcases/t/245-move-position-mouse.t
index 01e2c30e..2dd94938 100644
--- a/testcases/t/245-move-position-mouse.t
+++ b/testcases/t/245-move-position-mouse.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests the 'move [window|container] [to] position mouse|cursor|pointer command.
diff --git a/testcases/t/246-window-decoration-focus.t b/testcases/t/246-window-decoration-focus.t
index 265cb87a..197a66c5 100644
--- a/testcases/t/246-window-decoration-focus.t
+++ b/testcases/t/246-window-decoration-focus.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Ensure that hovering over the window decoration of a window causes it to focus
diff --git a/testcases/t/247-config-line-continuation.t b/testcases/t/247-config-line-continuation.t
index c54f1ac4..1c32bedb 100644
--- a/testcases/t/247-config-line-continuation.t
+++ b/testcases/t/247-config-line-continuation.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Checks that the line continuation are parsed correctly
diff --git a/testcases/t/248-regress-urgency-clear.t b/testcases/t/248-regress-urgency-clear.t
index cb700c0e..99932170 100644
--- a/testcases/t/248-regress-urgency-clear.t
+++ b/testcases/t/248-regress-urgency-clear.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Ensures the urgency hint is cleared properly in the case where i3 set it (due
diff --git a/testcases/t/249-layout-restore-floating.t b/testcases/t/249-layout-restore-floating.t
index 61cfda5c..8b6576a2 100644
--- a/testcases/t/249-layout-restore-floating.t
+++ b/testcases/t/249-layout-restore-floating.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies floating containers are restored in the correct place in the
diff --git a/testcases/t/250-layout-restore-multiple-criteria.t b/testcases/t/250-layout-restore-multiple-criteria.t
index 10a6d771..51d28d81 100644
--- a/testcases/t/250-layout-restore-multiple-criteria.t
+++ b/testcases/t/250-layout-restore-multiple-criteria.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # TODO: Description of this file.
diff --git a/testcases/t/251-command-criteria-focused.t b/testcases/t/251-command-criteria-focused.t
index a880f591..80bcfb65 100644
--- a/testcases/t/251-command-criteria-focused.t
+++ b/testcases/t/251-command-criteria-focused.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests for the special value "__focused__" in command criteria.
diff --git a/testcases/t/252-floating-size.t b/testcases/t/252-floating-size.t
index 5c746de9..51c36b29 100644
--- a/testcases/t/252-floating-size.t
+++ b/testcases/t/252-floating-size.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test behavior of "resize <width> <height>" command.
diff --git a/testcases/t/253-multiple-net-wm-state-atoms.t b/testcases/t/253-multiple-net-wm-state-atoms.t
index 3a3e7c6e..3e67e6b0 100644
--- a/testcases/t/253-multiple-net-wm-state-atoms.t
+++ b/testcases/t/253-multiple-net-wm-state-atoms.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Ticket: #1873
diff --git a/testcases/t/254-move-to-output-with-criteria.t b/testcases/t/254-move-to-output-with-criteria.t
index c129aa71..775965cd 100644
--- a/testcases/t/254-move-to-output-with-criteria.t
+++ b/testcases/t/254-move-to-output-with-criteria.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that "move container to output" works correctly when
diff --git a/testcases/t/255-multiple-marks.t b/testcases/t/255-multiple-marks.t
index 61fac006..e680c0c7 100644
--- a/testcases/t/255-multiple-marks.t
+++ b/testcases/t/255-multiple-marks.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests for mark/unmark with multiple marks on a single window.
diff --git a/testcases/t/256-no-auto-back-and-forth.t b/testcases/t/256-no-auto-back-and-forth.t
index 4242b430..9736a81a 100644
--- a/testcases/t/256-no-auto-back-and-forth.t
+++ b/testcases/t/256-no-auto-back-and-forth.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test for the --no-auto-back-and-forth flag.
diff --git a/testcases/t/257-keypress-group1-fallback.t b/testcases/t/257-keypress-group1-fallback.t
index bc08aa2f..6a1bc73a 100644
--- a/testcases/t/257-keypress-group1-fallback.t
+++ b/testcases/t/257-keypress-group1-fallback.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that when using multiple keyboard layouts at the same time, bindings
diff --git a/testcases/t/258-keypress-release.t b/testcases/t/258-keypress-release.t
index 614164ab..78b1e905 100644
--- a/testcases/t/258-keypress-release.t
+++ b/testcases/t/258-keypress-release.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that --release key bindings are not shadowed by non-release key
diff --git a/testcases/t/259-net-wm-user-time.t b/testcases/t/259-net-wm-user-time.t
index c1182616..fab55e06 100644
--- a/testcases/t/259-net-wm-user-time.t
+++ b/testcases/t/259-net-wm-user-time.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test for _NET_WM_USER_TIME.
diff --git a/testcases/t/260-invalid-criteria.t b/testcases/t/260-invalid-criteria.t
index b8cc2f1f..3d2cb108 100644
--- a/testcases/t/260-invalid-criteria.t
+++ b/testcases/t/260-invalid-criteria.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Ticket: #2091
diff --git a/testcases/t/261-match-con_id-con_mark-combinations.t b/testcases/t/261-match-con_id-con_mark-combinations.t
index efc62ba0..a34dbfa5 100644
--- a/testcases/t/261-match-con_id-con_mark-combinations.t
+++ b/testcases/t/261-match-con_id-con_mark-combinations.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Ticket: #2111
diff --git a/testcases/t/262-config-validation.t b/testcases/t/262-config-validation.t
index d4df70c7..4cbc69fd 100644
--- a/testcases/t/262-config-validation.t
+++ b/testcases/t/262-config-validation.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Ensures that calling i3 with the -C switch works (smoke test).
diff --git a/testcases/t/263-config-reload-reverts-bind-mode.t b/testcases/t/263-config-reload-reverts-bind-mode.t
index 1416b6b9..cce4f959 100644
--- a/testcases/t/263-config-reload-reverts-bind-mode.t
+++ b/testcases/t/263-config-reload-reverts-bind-mode.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that reloading the config reverts to the default
diff --git a/testcases/t/264-dock-criteria.t b/testcases/t/264-dock-criteria.t
index fe482409..a12d7bbe 100644
--- a/testcases/t/264-dock-criteria.t
+++ b/testcases/t/264-dock-criteria.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that command or config criteria does not match dock clients
diff --git a/testcases/t/265-ipc-mark.t b/testcases/t/265-ipc-mark.t
index a101944e..1930559f 100644
--- a/testcases/t/265-ipc-mark.t
+++ b/testcases/t/265-ipc-mark.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests for the window::mark IPC event.
diff --git a/testcases/t/266-net-moveresize-window.t b/testcases/t/266-net-moveresize-window.t
index b31aeed6..2c437614 100644
--- a/testcases/t/266-net-moveresize-window.t
+++ b/testcases/t/266-net-moveresize-window.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests for _NET_MOVERESIZE_WINDOW.
diff --git a/testcases/t/267-regress-mark-restart.t b/testcases/t/267-regress-mark-restart.t
index fe22e70c..d2a016bb 100644
--- a/testcases/t/267-regress-mark-restart.t
+++ b/testcases/t/267-regress-mark-restart.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test to check if mark and restart commands crash i3
diff --git a/testcases/t/268-ipc-config.t b/testcases/t/268-ipc-config.t
index 9ac749b6..c3f36b1c 100644
--- a/testcases/t/268-ipc-config.t
+++ b/testcases/t/268-ipc-config.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that the config file is returned raw via the IPC interface.
diff --git a/testcases/t/269-focus-stack-above.t b/testcases/t/269-focus-stack-above.t
index 66034211..2497432a 100644
--- a/testcases/t/269-focus-stack-above.t
+++ b/testcases/t/269-focus-stack-above.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies a ConfigureWindow request with stack-mode=Above is translated into
diff --git a/testcases/t/270-config-no-newline-end.t b/testcases/t/270-config-no-newline-end.t
index 24c017f2..8cd99ce8 100644
--- a/testcases/t/270-config-no-newline-end.t
+++ b/testcases/t/270-config-no-newline-end.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Make sure that configs that end without a newline don't crash i3.
diff --git a/testcases/t/271-for_window_tilingfloating.t b/testcases/t/271-for_window_tilingfloating.t
index f11908ab..94684452 100644
--- a/testcases/t/271-for_window_tilingfloating.t
+++ b/testcases/t/271-for_window_tilingfloating.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 use i3test i3_autostart => 0;
diff --git a/testcases/t/272-regress-focus-assign.t b/testcases/t/272-regress-focus-assign.t
index 44b188af..fb1ffa17 100644
--- a/testcases/t/272-regress-focus-assign.t
+++ b/testcases/t/272-regress-focus-assign.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression: Checks if focus is stolen when a window is managed which is
diff --git a/testcases/t/273-regress-focus-toggle.t b/testcases/t/273-regress-focus-toggle.t
index b51d74b6..50a7bbec 100644
--- a/testcases/t/273-regress-focus-toggle.t
+++ b/testcases/t/273-regress-focus-toggle.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression: Checks if i3 still lives after using 'focus mode_toggle' on an
diff --git a/testcases/t/274-move-branch-position.t b/testcases/t/274-move-branch-position.t
index e4d97819..50a39388 100644
--- a/testcases/t/274-move-branch-position.t
+++ b/testcases/t/274-move-branch-position.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that movement of a con into a branch will place the moving con at the
diff --git a/testcases/t/275-ipc-window-close.t b/testcases/t/275-ipc-window-close.t
index ccaf4440..ab258256 100644
--- a/testcases/t/275-ipc-window-close.t
+++ b/testcases/t/275-ipc-window-close.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that the ipc close event works properly
diff --git a/testcases/t/276-ipc-window-move.t b/testcases/t/276-ipc-window-move.t
index 708963df..561633ab 100644
--- a/testcases/t/276-ipc-window-move.t
+++ b/testcases/t/276-ipc-window-move.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that the ipc window::move event works properly
diff --git a/testcases/t/277-ipc-window-urgent.t b/testcases/t/277-ipc-window-urgent.t
index 4eea2cdc..2789c07f 100644
--- a/testcases/t/277-ipc-window-urgent.t
+++ b/testcases/t/277-ipc-window-urgent.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that the window::urgent event works correctly. The window::urgent event
diff --git a/testcases/t/278-layout-restore-output.t b/testcases/t/278-layout-restore-output.t
index e87cfa8b..06a31fbd 100644
--- a/testcases/t/278-layout-restore-output.t
+++ b/testcases/t/278-layout-restore-output.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that entire outputs can be saved and restored properly by i3.
diff --git a/testcases/t/279-regress-default-floating-border.t b/testcases/t/279-regress-default-floating-border.t
index ba905b9c..03e8298b 100644
--- a/testcases/t/279-regress-default-floating-border.t
+++ b/testcases/t/279-regress-default-floating-border.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # This is a regression test for a bug where a normal floating default border is
diff --git a/testcases/t/280-wm-class-change-handler.t b/testcases/t/280-wm-class-change-handler.t
index 90268bd3..10a7ef85 100644
--- a/testcases/t/280-wm-class-change-handler.t
+++ b/testcases/t/280-wm-class-change-handler.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that changes to WM_CLASS are internally processed by i3 by updating the
diff --git a/testcases/t/281-regress-reload-bindsym.t b/testcases/t/281-regress-reload-bindsym.t
index 27b00245..2bc7d2c1 100644
--- a/testcases/t/281-regress-reload-bindsym.t
+++ b/testcases/t/281-regress-reload-bindsym.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that the binding event works properly
diff --git a/testcases/t/282-tabbed-floating-disable-crash.t b/testcases/t/282-tabbed-floating-disable-crash.t
index c7eebd7e..5734037d 100644
--- a/testcases/t/282-tabbed-floating-disable-crash.t
+++ b/testcases/t/282-tabbed-floating-disable-crash.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that i3 does not crash when floating and then unfloating an
diff --git a/testcases/t/283-net-wm-state-hidden.t b/testcases/t/283-net-wm-state-hidden.t
index 102a3ffc..d6c7b2f8 100644
--- a/testcases/t/283-net-wm-state-hidden.t
+++ b/testcases/t/283-net-wm-state-hidden.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests for setting and removing the _NET_WM_STATE_HIDDEN atom properly.
diff --git a/testcases/t/284-ewmh-visible-name.t b/testcases/t/284-ewmh-visible-name.t
index c83b019a..f2072b5b 100644
--- a/testcases/t/284-ewmh-visible-name.t
+++ b/testcases/t/284-ewmh-visible-name.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that _NET_WM_VISIBLE_NAME is set correctly.
diff --git a/testcases/t/285-sticky.t b/testcases/t/285-sticky.t
index 8dfe9aea..62fe7544 100644
--- a/testcases/t/285-sticky.t
+++ b/testcases/t/285-sticky.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests sticky windows.
diff --git a/testcases/t/286-root-window-mouse-binding.t b/testcases/t/286-root-window-mouse-binding.t
index 0da373b7..9b5cce07 100644
--- a/testcases/t/286-root-window-mouse-binding.t
+++ b/testcases/t/286-root-window-mouse-binding.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that mouse bindings work on the root window if
diff --git a/testcases/t/287-edge-borders.t b/testcases/t/287-edge-borders.t
index 3dfc3407..eb4c18c8 100644
--- a/testcases/t/287-edge-borders.t
+++ b/testcases/t/287-edge-borders.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that the hide_edge_borders smart option works
diff --git a/testcases/t/288-i3-floating-window-atom.t b/testcases/t/288-i3-floating-window-atom.t
index 4b90dc82..e66bf22c 100644
--- a/testcases/t/288-i3-floating-window-atom.t
+++ b/testcases/t/288-i3-floating-window-atom.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests for our proprietary atom I3_FLOATING_WINDOW to allow
diff --git a/testcases/t/289-ipc-shutdown-event.t b/testcases/t/289-ipc-shutdown-event.t
index a56c4ac7..68fc1fb8 100644
--- a/testcases/t/289-ipc-shutdown-event.t
+++ b/testcases/t/289-ipc-shutdown-event.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test the ipc shutdown event. This event is triggered when the connection to
diff --git a/testcases/t/290-keypress-numlock.t b/testcases/t/290-keypress-numlock.t
index 94a5747d..ab703713 100644
--- a/testcases/t/290-keypress-numlock.t
+++ b/testcases/t/290-keypress-numlock.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that one can bind on numpad keys in different numlock states.
diff --git a/testcases/t/291-swap.t b/testcases/t/291-swap.t
index 781315e5..6ca98216 100644
--- a/testcases/t/291-swap.t
+++ b/testcases/t/291-swap.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests the swap command.
diff --git a/testcases/t/292-regress-layout-toggle.t b/testcases/t/292-regress-layout-toggle.t
index e34faddd..aae911f5 100644
--- a/testcases/t/292-regress-layout-toggle.t
+++ b/testcases/t/292-regress-layout-toggle.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test: verify layout toggle with invalid parameters does not set
diff --git a/testcases/t/293-focus-follows-mouse.t b/testcases/t/293-focus-follows-mouse.t
index 55958c3e..2fb62513 100644
--- a/testcases/t/293-focus-follows-mouse.t
+++ b/testcases/t/293-focus-follows-mouse.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests the focus_follows_mouse setting.
diff --git a/testcases/t/293-sticky-output-crash.t b/testcases/t/293-sticky-output-crash.t
index 93ebaee9..628d74db 100644
--- a/testcases/t/293-sticky-output-crash.t
+++ b/testcases/t/293-sticky-output-crash.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that i3 does not crash when opening a floating sticky on one output
diff --git a/testcases/t/294-focus-order.t b/testcases/t/294-focus-order.t
index dfadd0af..23427230 100644
--- a/testcases/t/294-focus-order.t
+++ b/testcases/t/294-focus-order.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verify that the current focus stack order is preserved after various
diff --git a/testcases/t/294-update-ewmh-atoms.t b/testcases/t/294-update-ewmh-atoms.t
index f13b1764..1a67c0ce 100644
--- a/testcases/t/294-update-ewmh-atoms.t
+++ b/testcases/t/294-update-ewmh-atoms.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies _NET_DESKTOP_NAMES, _NET_CURRENT_DESKTOP and _NET_CURRENT_DESKTOP
diff --git a/testcases/t/295-net-wm-state-focused.t b/testcases/t/295-net-wm-state-focused.t
index fd7c2513..68283e9c 100644
--- a/testcases/t/295-net-wm-state-focused.t
+++ b/testcases/t/295-net-wm-state-focused.t
@@ -11,7 +11,7 @@
 # • http://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests for setting and removing the _NET_WM_STATE_FOCUSED atom properly.
diff --git a/testcases/t/296-regress-focus-behind-fullscreen-floating.t b/testcases/t/296-regress-focus-behind-fullscreen-floating.t
index 0867f082..4f942355 100644
--- a/testcases/t/296-regress-focus-behind-fullscreen-floating.t
+++ b/testcases/t/296-regress-focus-behind-fullscreen-floating.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that directional focus gives focus to floating fullscreen containers when
diff --git a/testcases/t/297-assign-workspace-to-output.t b/testcases/t/297-assign-workspace-to-output.t
index 68aa1f89..06caf96a 100644
--- a/testcases/t/297-assign-workspace-to-output.t
+++ b/testcases/t/297-assign-workspace-to-output.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test assignments of workspaces to outputs.
diff --git a/testcases/t/297-scroll-tabbed.t b/testcases/t/297-scroll-tabbed.t
index c47b5315..0d5066d5 100644
--- a/testcases/t/297-scroll-tabbed.t
+++ b/testcases/t/297-scroll-tabbed.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests if scrolling the tab bar on a tabbed container works and verifies that
diff --git a/testcases/t/298-ipc-misbehaving-connection.t b/testcases/t/298-ipc-misbehaving-connection.t
index d53ee92d..fe4fe523 100644
--- a/testcases/t/298-ipc-misbehaving-connection.t
+++ b/testcases/t/298-ipc-misbehaving-connection.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that i3 will not hang if a connected client stops reading from its
diff --git a/testcases/t/299-regress-scratchpad-focus.t b/testcases/t/299-regress-scratchpad-focus.t
index 504ecd32..2eb14972 100644
--- a/testcases/t/299-regress-scratchpad-focus.t
+++ b/testcases/t/299-regress-scratchpad-focus.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression test: verify that a scratchpad container that was open in another
diff --git a/testcases/t/300-restart-non-utf8.t b/testcases/t/300-restart-non-utf8.t
index 81b56583..50dbad59 100644
--- a/testcases/t/300-restart-non-utf8.t
+++ b/testcases/t/300-restart-non-utf8.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verify that i3 does not crash when restart is issued while a window with a
diff --git a/testcases/t/301-shape.t b/testcases/t/301-shape.t
index b18ac0ca..c9bf1681 100644
--- a/testcases/t/301-shape.t
+++ b/testcases/t/301-shape.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test shape support.
diff --git a/testcases/t/302-tree.t b/testcases/t/302-tree.t
index a2551a3e..8003bc67 100644
--- a/testcases/t/302-tree.t
+++ b/testcases/t/302-tree.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Contains various tests that use the cmp_tree subroutine.
diff --git a/testcases/t/303-regress-move-floating.t b/testcases/t/303-regress-move-floating.t
index 396e586f..f742bc16 100644
--- a/testcases/t/303-regress-move-floating.t
+++ b/testcases/t/303-regress-move-floating.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Regression: moving a container which is the only child of the only child of a
diff --git a/testcases/t/304-ipc-workspace-init.t b/testcases/t/304-ipc-workspace-init.t
index 4c181f7c..4b6136ea 100644
--- a/testcases/t/304-ipc-workspace-init.t
+++ b/testcases/t/304-ipc-workspace-init.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that the workspace init event is correctly sent.
diff --git a/testcases/t/305-restart-reply.t b/testcases/t/305-restart-reply.t
index 0493d4ff..03db3c3b 100644
--- a/testcases/t/305-restart-reply.t
+++ b/testcases/t/305-restart-reply.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verify that restart produces a reply.
diff --git a/testcases/t/306-move-to-parent.t b/testcases/t/306-move-to-parent.t
index 8610cff9..ae1257d7 100644
--- a/testcases/t/306-move-to-parent.t
+++ b/testcases/t/306-move-to-parent.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Make sure the trick used to move the container to its parent works.
diff --git a/testcases/t/307-focus-next-prev.t b/testcases/t/307-focus-next-prev.t
index 4f8a8ecd..618c170a 100644
--- a/testcases/t/307-focus-next-prev.t
+++ b/testcases/t/307-focus-next-prev.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test focus next|prev
diff --git a/testcases/t/308-focus_wrapping.t b/testcases/t/308-focus_wrapping.t
index 9fa5858c..18d426bb 100644
--- a/testcases/t/308-focus_wrapping.t
+++ b/testcases/t/308-focus_wrapping.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests focus_wrapping yes|no|force|workspace with cmp_tree
diff --git a/testcases/t/309-crash-move-parent.t b/testcases/t/309-crash-move-parent.t
index eb58251b..423af0f2 100644
--- a/testcases/t/309-crash-move-parent.t
+++ b/testcases/t/309-crash-move-parent.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that moving a container that is to be flattened does not crash i3
diff --git a/testcases/t/310-client-message-sticky.t b/testcases/t/310-client-message-sticky.t
index 0e7d8b7c..f815d6b1 100644
--- a/testcases/t/310-client-message-sticky.t
+++ b/testcases/t/310-client-message-sticky.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verify that _NET_WM_DESKTOP sticky requests do not conflict with dock
diff --git a/testcases/t/311-get-binding-modes.t b/testcases/t/311-get-binding-modes.t
index 3a00f695..1d77d43d 100644
--- a/testcases/t/311-get-binding-modes.t
+++ b/testcases/t/311-get-binding-modes.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies the GET_BINDING_MODE IPC command
diff --git a/testcases/t/312-regress-layout-default.t b/testcases/t/312-regress-layout-default.t
index b23cf50b..ade1bc4b 100644
--- a/testcases/t/312-regress-layout-default.t
+++ b/testcases/t/312-regress-layout-default.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies i3 does not crash when using layout default.
diff --git a/testcases/t/313-include.t b/testcases/t/313-include.t
index 9b8b0fab..dc89eb5c 100644
--- a/testcases/t/313-include.t
+++ b/testcases/t/313-include.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies the include directive.
diff --git a/testcases/t/314-window-icon-padding.t b/testcases/t/314-window-icon-padding.t
index 71cf5bd5..a1a9c07e 100755
--- a/testcases/t/314-window-icon-padding.t
+++ b/testcases/t/314-window-icon-padding.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies title_window_icon behavior.
diff --git a/testcases/t/315-all-criterion.t b/testcases/t/315-all-criterion.t
index f11410fd..11744cd9 100644
--- a/testcases/t/315-all-criterion.t
+++ b/testcases/t/315-all-criterion.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests all kinds of matching methods
diff --git a/testcases/t/315-long-commands.t b/testcases/t/315-long-commands.t
index 3db37dab..4b51d791 100644
--- a/testcases/t/315-long-commands.t
+++ b/testcases/t/315-long-commands.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that commands with more than 10 non-identified words doesn't works
diff --git a/testcases/t/316-drag-container.t b/testcases/t/316-drag-container.t
index 7e2b8494..4a217d46 100644
--- a/testcases/t/316-drag-container.t
+++ b/testcases/t/316-drag-container.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test dragging containers.
diff --git a/testcases/t/316-transient-for-loop.t b/testcases/t/316-transient-for-loop.t
index 336a8d8d..ceb2713d 100644
--- a/testcases/t/316-transient-for-loop.t
+++ b/testcases/t/316-transient-for-loop.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that i3 does not get stuck in an endless loop between two windows that
diff --git a/testcases/t/317-bar-config-font-order.t b/testcases/t/317-bar-config-font-order.t
index 3c1fdcdd..72782152 100644
--- a/testcases/t/317-bar-config-font-order.t
+++ b/testcases/t/317-bar-config-font-order.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that bar config blocks get the i3-wide font configured,
diff --git a/testcases/t/317-bar-output-trailing-space.t b/testcases/t/317-bar-output-trailing-space.t
index 540d30c9..5f266230 100644
--- a/testcases/t/317-bar-output-trailing-space.t
+++ b/testcases/t/317-bar-output-trailing-space.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that any trailing whitespace in strings (including in
diff --git a/testcases/t/318-i3-dmenu-desktop.t b/testcases/t/318-i3-dmenu-desktop.t
index 2ad7f41b..9ccef925 100644
--- a/testcases/t/318-i3-dmenu-desktop.t
+++ b/testcases/t/318-i3-dmenu-desktop.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that i3-dmenu-desktop correctly parses Exec= lines in .desktop files
diff --git a/testcases/t/319-gaps.t b/testcases/t/319-gaps.t
index fa723dfc..fff01fb0 100644
--- a/testcases/t/319-gaps.t
+++ b/testcases/t/319-gaps.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Basic gaps functionality test
diff --git a/testcases/t/320-mouse-bindings.t b/testcases/t/320-mouse-bindings.t
index 45e0f4ff..b1e81228 100644
--- a/testcases/t/320-mouse-bindings.t
+++ b/testcases/t/320-mouse-bindings.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test button bindsyms
diff --git a/testcases/t/500-multi-monitor.t b/testcases/t/500-multi-monitor.t
index 8d2c6496..2f647247 100644
--- a/testcases/t/500-multi-monitor.t
+++ b/testcases/t/500-multi-monitor.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that the provided X-Server to the t/5??-*.t tests is actually providing
diff --git a/testcases/t/501-scratchpad.t b/testcases/t/501-scratchpad.t
index 3b7fa90c..52858718 100644
--- a/testcases/t/501-scratchpad.t
+++ b/testcases/t/501-scratchpad.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that scratchpad windows show up on the proper output.
diff --git a/testcases/t/502-focus-output.t b/testcases/t/502-focus-output.t
index 5b051de4..c13e7e14 100644
--- a/testcases/t/502-focus-output.t
+++ b/testcases/t/502-focus-output.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies the 'focus output' command works properly.
diff --git a/testcases/t/503-workspace.t b/testcases/t/503-workspace.t
index cb0ad92f..04ac8a59 100644
--- a/testcases/t/503-workspace.t
+++ b/testcases/t/503-workspace.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests whether 'workspace next_on_output' and the like work correctly.
diff --git a/testcases/t/504-move-workspace-to-output.t b/testcases/t/504-move-workspace-to-output.t
index 4ec33f66..f6b5e9f8 100644
--- a/testcases/t/504-move-workspace-to-output.t
+++ b/testcases/t/504-move-workspace-to-output.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests whether the 'move workspace <ws> to [output] <output>' command works
diff --git a/testcases/t/505-scratchpad-resolution.t b/testcases/t/505-scratchpad-resolution.t
index e72b4dfb..fc4758fa 100644
--- a/testcases/t/505-scratchpad-resolution.t
+++ b/testcases/t/505-scratchpad-resolution.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that scratchpad windows don’t move due to floating point caulcation
diff --git a/testcases/t/506-focus-right.t b/testcases/t/506-focus-right.t
index 2d8ed205..aa436b23 100644
--- a/testcases/t/506-focus-right.t
+++ b/testcases/t/506-focus-right.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that focus output right works with monitor setups that don’t line up
diff --git a/testcases/t/507-workspace-move-crash.t b/testcases/t/507-workspace-move-crash.t
index 7adbb6e2..a3141300 100644
--- a/testcases/t/507-workspace-move-crash.t
+++ b/testcases/t/507-workspace-move-crash.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests whether i3 crashes on cross-output moves with one workspace per output.
diff --git a/testcases/t/509-workspace_layout.t b/testcases/t/509-workspace_layout.t
index 40e7e881..2a4131d4 100644
--- a/testcases/t/509-workspace_layout.t
+++ b/testcases/t/509-workspace_layout.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests whether workspace_layout is properly set after startup.
diff --git a/testcases/t/510-focus-across-outputs.t b/testcases/t/510-focus-across-outputs.t
index 065437f0..621119bb 100644
--- a/testcases/t/510-focus-across-outputs.t
+++ b/testcases/t/510-focus-across-outputs.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that switching workspaces via 'focus $dir' never leaves a floating
diff --git a/testcases/t/511-scratchpad-configure-request.t b/testcases/t/511-scratchpad-configure-request.t
index 0a06c070..7dd76108 100644
--- a/testcases/t/511-scratchpad-configure-request.t
+++ b/testcases/t/511-scratchpad-configure-request.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that ConfigureRequests don’t make windows fall out of the scratchpad.
diff --git a/testcases/t/512-move-wraps.t b/testcases/t/512-move-wraps.t
index d346a176..8f2324b9 100644
--- a/testcases/t/512-move-wraps.t
+++ b/testcases/t/512-move-wraps.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that moving containers wraps across outputs.
diff --git a/testcases/t/513-move-workspace.t b/testcases/t/513-move-workspace.t
index db8890a9..f2ffbdf6 100644
--- a/testcases/t/513-move-workspace.t
+++ b/testcases/t/513-move-workspace.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests whether moving workspaces between outputs works correctly.
diff --git a/testcases/t/514-ipc-workspace-multi-monitor.t b/testcases/t/514-ipc-workspace-multi-monitor.t
index ac918fe3..c12e3046 100644
--- a/testcases/t/514-ipc-workspace-multi-monitor.t
+++ b/testcases/t/514-ipc-workspace-multi-monitor.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Ticket: #990
diff --git a/testcases/t/515-create-workspace.t b/testcases/t/515-create-workspace.t
index e90cf66a..2d10a4eb 100644
--- a/testcases/t/515-create-workspace.t
+++ b/testcases/t/515-create-workspace.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that new workspace names are taken from the config,
diff --git a/testcases/t/516-move.t b/testcases/t/516-move.t
index 3db8c4f0..29606c9e 100644
--- a/testcases/t/516-move.t
+++ b/testcases/t/516-move.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests if a simple 'move <direction>' command will move containers across outputs.
diff --git a/testcases/t/517-regress-move-direction-ipc.t b/testcases/t/517-regress-move-direction-ipc.t
index 2f7f2b27..5a1010e1 100644
--- a/testcases/t/517-regress-move-direction-ipc.t
+++ b/testcases/t/517-regress-move-direction-ipc.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Make sure the command `move <direction>` properly sends the workspace focus
diff --git a/testcases/t/518-interpret-workspace-numbers.t b/testcases/t/518-interpret-workspace-numbers.t
index c7ab8367..d51b708c 100644
--- a/testcases/t/518-interpret-workspace-numbers.t
+++ b/testcases/t/518-interpret-workspace-numbers.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that workspace assignment config directives for plain numbers will
diff --git a/testcases/t/519-mouse-warping.t b/testcases/t/519-mouse-warping.t
index 3cfb1ec2..193982fd 100644
--- a/testcases/t/519-mouse-warping.t
+++ b/testcases/t/519-mouse-warping.t
@@ -8,7 +8,7 @@
 # • https://build.i3wm.org/docs/lib-i3test.html
 #   (alternatively: perldoc ./testcases/lib/i3test.pm)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 
 use i3test i3_config => <<EOT;
diff --git a/testcases/t/520-regress-focus-direction-floating.t b/testcases/t/520-regress-focus-direction-floating.t
index 74da7489..cec9c866 100644
--- a/testcases/t/520-regress-focus-direction-floating.t
+++ b/testcases/t/520-regress-focus-direction-floating.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Ensure that `focus [direction]` will focus an existing floating con when no
diff --git a/testcases/t/521-ewmh-desktop-viewport.t b/testcases/t/521-ewmh-desktop-viewport.t
index a4119367..fb050aac 100644
--- a/testcases/t/521-ewmh-desktop-viewport.t
+++ b/testcases/t/521-ewmh-desktop-viewport.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that the EWMH specified property _NET_DESKTOP_VIEWPORT is updated
diff --git a/testcases/t/522-rename-assigned-workspace.t b/testcases/t/522-rename-assigned-workspace.t
index 9897e4ee..a9e0d04c 100644
--- a/testcases/t/522-rename-assigned-workspace.t
+++ b/testcases/t/522-rename-assigned-workspace.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 #
diff --git a/testcases/t/523-move-position-center.t b/testcases/t/523-move-position-center.t
index cf4e5070..eda7c9cf 100644
--- a/testcases/t/523-move-position-center.t
+++ b/testcases/t/523-move-position-center.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies that 'move position center' moves floating cons to the center of
diff --git a/testcases/t/524-move.t b/testcases/t/524-move.t
index e880b18e..b9ae6098 100644
--- a/testcases/t/524-move.t
+++ b/testcases/t/524-move.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests the behaviour of 'move <direction>' when moving containers across
diff --git a/testcases/t/525-i3bar-mouse-bindings.t b/testcases/t/525-i3bar-mouse-bindings.t
index 3593ea0b..b8055746 100644
--- a/testcases/t/525-i3bar-mouse-bindings.t
+++ b/testcases/t/525-i3bar-mouse-bindings.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Ensures that mouse bindings on the i3bar work correctly.
diff --git a/testcases/t/526-reconfigure-dock.t b/testcases/t/526-reconfigure-dock.t
index 97e98a60..ad64e77f 100644
--- a/testcases/t/526-reconfigure-dock.t
+++ b/testcases/t/526-reconfigure-dock.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test reconfiguration of dock clients.
diff --git a/testcases/t/527-focus-fallback.t b/testcases/t/527-focus-fallback.t
index 531e1854..ca22fcab 100644
--- a/testcases/t/527-focus-fallback.t
+++ b/testcases/t/527-focus-fallback.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Ticket: #1378
diff --git a/testcases/t/528-workspace-next-prev-reversed.t b/testcases/t/528-workspace-next-prev-reversed.t
index 4f63e7fe..b58457b8 100644
--- a/testcases/t/528-workspace-next-prev-reversed.t
+++ b/testcases/t/528-workspace-next-prev-reversed.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests whether 'workspace next' works correctly.
diff --git a/testcases/t/529-net-wm-desktop.t b/testcases/t/529-net-wm-desktop.t
index f1da2980..d9827326 100644
--- a/testcases/t/529-net-wm-desktop.t
+++ b/testcases/t/529-net-wm-desktop.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests for _NET_WM_DESKTOP.
diff --git a/testcases/t/530-bug-2229.t b/testcases/t/530-bug-2229.t
index a177ee3c..15a405a3 100644
--- a/testcases/t/530-bug-2229.t
+++ b/testcases/t/530-bug-2229.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Ticket: #2229
diff --git a/testcases/t/531-fullscreen-on-given-output.t b/testcases/t/531-fullscreen-on-given-output.t
index 2459f06c..fec9952e 100644
--- a/testcases/t/531-fullscreen-on-given-output.t
+++ b/testcases/t/531-fullscreen-on-given-output.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that fullscreen windows appear on the output indicated by
diff --git a/testcases/t/532-xresources.t b/testcases/t/532-xresources.t
index 1ff48e51..7acd99e7 100644
--- a/testcases/t/532-xresources.t
+++ b/testcases/t/532-xresources.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests for using X resources in the config.
diff --git a/testcases/t/533-randr15.t b/testcases/t/533-randr15.t
index 51d1c9f6..9e8f2e8a 100644
--- a/testcases/t/533-randr15.t
+++ b/testcases/t/533-randr15.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # TODO: Description of this file.
diff --git a/testcases/t/534-dont-warp.t b/testcases/t/534-dont-warp.t
index 8c943208..02cc8f75 100644
--- a/testcases/t/534-dont-warp.t
+++ b/testcases/t/534-dont-warp.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Verifies i3 doesn’t warp when a new floating window is opened under the cursor
diff --git a/testcases/t/535-workspace-next-prev.t b/testcases/t/535-workspace-next-prev.t
index dc881b35..0020586e 100644
--- a/testcases/t/535-workspace-next-prev.t
+++ b/testcases/t/535-workspace-next-prev.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests whether 'workspace next' works correctly.
diff --git a/testcases/t/536-net-wm-desktop_mm.t b/testcases/t/536-net-wm-desktop_mm.t
index 3e4c9747..cc037c37 100644
--- a/testcases/t/536-net-wm-desktop_mm.t
+++ b/testcases/t/536-net-wm-desktop_mm.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests for _NET_WM_DESKTOP.
diff --git a/testcases/t/537-move-single-to-output.t b/testcases/t/537-move-single-to-output.t
index ab144897..8693043e 100644
--- a/testcases/t/537-move-single-to-output.t
+++ b/testcases/t/537-move-single-to-output.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that windows inside containers with a single child do not jump
diff --git a/testcases/t/538-i3bar-primary-output.t b/testcases/t/538-i3bar-primary-output.t
index d5581dd8..fbb8d464 100644
--- a/testcases/t/538-i3bar-primary-output.t
+++ b/testcases/t/538-i3bar-primary-output.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that i3bars configured to use the primary output do not have
diff --git a/testcases/t/539-disable_focus_wrapping.t b/testcases/t/539-disable_focus_wrapping.t
index 8d2e8472..9c08e5f1 100644
--- a/testcases/t/539-disable_focus_wrapping.t
+++ b/testcases/t/539-disable_focus_wrapping.t
@@ -11,7 +11,7 @@
 # • http://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that focus does not wrap when focus_wrapping is disabled in
diff --git a/testcases/t/540-sigterm-cleanup.t b/testcases/t/540-sigterm-cleanup.t
index 5e5b9bf3..11e3cea7 100644
--- a/testcases/t/540-sigterm-cleanup.t
+++ b/testcases/t/540-sigterm-cleanup.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that the socket file is cleaned up properly after gracefully
diff --git a/testcases/t/541-resize-set-tiling.t b/testcases/t/541-resize-set-tiling.t
index 0298fecd..e5b9e99e 100644
--- a/testcases/t/541-resize-set-tiling.t
+++ b/testcases/t/541-resize-set-tiling.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests resizing tiling containers
diff --git a/testcases/t/542-layout-restore-remanage.t b/testcases/t/542-layout-restore-remanage.t
index 82ec84d0..10015065 100644
--- a/testcases/t/542-layout-restore-remanage.t
+++ b/testcases/t/542-layout-restore-remanage.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Tests that swallowing still works after a window gets managed and its property
diff --git a/testcases/t/543-move-workspace-to-multiple-outputs.t b/testcases/t/543-move-workspace-to-multiple-outputs.t
index 7b0f8c2b..46b90e22 100644
--- a/testcases/t/543-move-workspace-to-multiple-outputs.t
+++ b/testcases/t/543-move-workspace-to-multiple-outputs.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test using multiple outputs for 'move workspace to output …'
diff --git a/testcases/t/544-focus-multiple-outputs.t b/testcases/t/544-focus-multiple-outputs.t
index 2d09dfba..e91226b6 100644
--- a/testcases/t/544-focus-multiple-outputs.t
+++ b/testcases/t/544-focus-multiple-outputs.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test using multiple output for 'focus output …'
diff --git a/testcases/t/546-empty-bindcommand.t b/testcases/t/546-empty-bindcommand.t
index dae26293..27296e76 100644
--- a/testcases/t/546-empty-bindcommand.t
+++ b/testcases/t/546-empty-bindcommand.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that i3 doesn't crash if the binding command is empty.
diff --git a/testcases/t/547-explicit-mode-default.t b/testcases/t/547-explicit-mode-default.t
index a966c7f6..7f055ec3 100644
--- a/testcases/t/547-explicit-mode-default.t
+++ b/testcases/t/547-explicit-mode-default.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that explicitly defined default mode doesn't cause segfault.
diff --git a/testcases/t/547-nested-variables.t b/testcases/t/547-nested-variables.t
index 990a42e9..ee2428a0 100644
--- a/testcases/t/547-nested-variables.t
+++ b/testcases/t/547-nested-variables.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that i3 doesn't crash if the config contains nested variables.
diff --git a/testcases/t/548-motif-hints.t b/testcases/t/548-motif-hints.t
index 9fe890cf..1f0276fa 100644
--- a/testcases/t/548-motif-hints.t
+++ b/testcases/t/548-motif-hints.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Test that setting and unsetting motif hints updates window decorations
diff --git a/testcases/t/549-focus-wrapping-gaps.t b/testcases/t/549-focus-wrapping-gaps.t
index 135bea8c..f84e7326 100644
--- a/testcases/t/549-focus-wrapping-gaps.t
+++ b/testcases/t/549-focus-wrapping-gaps.t
@@ -11,7 +11,7 @@
 # • https://build.i3wm.org/docs/ipc.html
 #   (or docs/ipc)
 #
-# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+# • https://i3wm.org/downloads/modern_perl_a4.pdf
 #   (unless you are already familiar with Perl)
 #
 # Ensure focus wrapping works with negative gaps