diff --git a/fluid/CMakeLists.txt b/fluid/CMakeLists.txt
index 6162bb89e..bb3b9fe51 100644
--- a/fluid/CMakeLists.txt
+++ b/fluid/CMakeLists.txt
@@ -17,7 +17,8 @@
 # Targets that will be built: fluid and fluid-cmd (Windows)
 set(TARGETS fluid)
 
-# Source files for 'fluid-lib' = all source files except the main file (fluid.cxx)
+# Source files for 'fluid-lib' = all source files except the main files
+# (fluid.cxx and fluid.h)
 # Note: macOS (Xcode) needs at least one source file (fluid.cxx) to link the main
 # program fluid properly
 
@@ -116,7 +117,7 @@ if(APPLE AND NOT FLTK_BACKEND_X11)
 
   set(ICON_NAME fluid.icns)
   set(ICON_PATH "${CMAKE_CURRENT_SOURCE_DIR}/icons/${ICON_NAME}")
-  add_executable(fluid MACOSX_BUNDLE fluid.cxx ${ICON_PATH})
+  add_executable(fluid MACOSX_BUNDLE fluid.cxx fluid.h ${ICON_PATH})
 
   # create macOS bundle wrapper script
 
@@ -133,7 +134,7 @@ if(APPLE AND NOT FLTK_BACKEND_X11)
 else()
 
   # Option 'WIN32' builds a Windows GUI program, ignored on other platforms
-  add_executable(fluid WIN32 fluid.cxx)
+  add_executable(fluid WIN32 fluid.cxx fluid.h)
 
 endif()
 
@@ -144,7 +145,7 @@ target_link_libraries(fluid PRIVATE fluid-lib)
 
 if(WIN32)
   list(APPEND TARGETS fluid-cmd)
-  add_executable(fluid-cmd fluid.cxx)
+  add_executable(fluid-cmd fluid.cxx fluid.h)
   target_link_libraries(fluid-cmd PRIVATE fluid-lib)
   set(FLTK_FLUID_EXECUTABLE fltk::fluid-cmd)
 else()
diff --git a/fluid/CodeEditor.cxx b/fluid/CodeEditor.cxx
index 2243db2fe..2fffcd8bc 100644
--- a/fluid/CodeEditor.cxx
+++ b/fluid/CodeEditor.cxx
@@ -2,7 +2,7 @@
 // Code editor widget for the Fast Light Tool Kit (FLTK).
 // Syntax highlighting rewritten by erco@seriss.com 09/15/20.
 //
-// Copyright 1998-2023 by Bill Spitzak and others.
+// Copyright 1998-2024 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -28,13 +28,6 @@
 
 // ---- CodeEditor implementation
 
-/** \class CodeEditor
- A widget derived from Fl_Text_Editor that implements C++ code highlighting.
-
- CodeEditor is used in Fluid whenever the user can edit C++ source
- code or header text.
- */
-
 /**
  Lookup table for all supported styles.
  Every table entry describes a rendering style for the corresponding text.
@@ -263,14 +256,6 @@ void CodeEditor::textsize(Fl_Fontsize s) {
 
 // ---- CodeViewer implementation
 
-/** \class CodeViewer
- A widget derived from CodeEditor with highlighting for code blocks.
-
- This widget is used by the SourceView system to show the design's
- source and header code. The secondary highlighting show the text
- part that corresponds to the selected widget(s).
- */
-
 /**
  Create a CodeViewer widget.
  \param[in] X, Y, W, H position and size of the widget
diff --git a/fluid/CodeEditor.h b/fluid/CodeEditor.h
index 50908ebe5..9886705aa 100644
--- a/fluid/CodeEditor.h
+++ b/fluid/CodeEditor.h
@@ -2,7 +2,7 @@
 // Code editor widget for the Fast Light Tool Kit (FLTK).
 // Syntax highlighting rewritten by erco@seriss.com 09/15/20.
 //
-// Copyright 1998-2022 by Bill Spitzak and others.
+// Copyright 1998-2024 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -35,6 +35,12 @@
 
 // ---- CodeEditor declaration
 
+/**
+ A widget derived from Fl_Text_Editor that implements C++ code highlighting.
+
+ CodeEditor is used in Fluid whenever the user can edit C++ source
+ code or header text.
+ */
 class CodeEditor : public Fl_Text_Editor {
   friend class StyleParse;
 
@@ -49,31 +55,51 @@ class CodeEditor : public Fl_Text_Editor {
 public:
   CodeEditor(int X, int Y, int W, int H, const char *L=0);
   ~CodeEditor();
-  int top_line() { return get_absolute_top_line_number(); }
   void textsize(Fl_Fontsize s);
+
+  /// access to protected member get_absolute_top_line_number()
+  int top_line() { return get_absolute_top_line_number(); }
+
+  /// access to protected member mTopLineNum
   int scroll_row() { return mTopLineNum; }
+
+  /// access to protected member mHorizOffset
   int scroll_col() { return mHorizOffset; }
 };
 
 // ---- CodeViewer declaration
 
+/**
+ A widget derived from CodeEditor with highlighting for code blocks.
+
+ This widget is used by the SourceView system to show the design's
+ source and header code. The secondary highlighting show the text
+ part that corresponds to the selected widget(s).
+ */
 class CodeViewer : public CodeEditor {
 public:
   CodeViewer(int X, int Y, int W, int H, const char *L=0);
 
 protected:
-  int handle(int ev)  FL_OVERRIDE{ return Fl_Text_Display::handle(ev); }
   void draw() FL_OVERRIDE;
+
+  /// Limit event handling to viewing, not editing
+  int handle(int ev) FL_OVERRIDE { return Fl_Text_Display::handle(ev); }
 };
 
-// ---- Project File Text Viewe declaration
+// ---- Project File Text Viewer declaration
 
+/**
+ A text viewer with an additional highlighting color scheme.
+ */
 class TextViewer : public Fl_Text_Display {
 public:
   TextViewer(int X, int Y, int W, int H, const char *L=0);
   ~TextViewer();
-  int top_line() { return get_absolute_top_line_number(); }
   void draw() FL_OVERRIDE;
+
+  /// access to protected member get_absolute_top_line_number()
+  int top_line() { return get_absolute_top_line_number(); }
 };
 
 #endif // !CodeEditor_h
diff --git a/fluid/Fd_Snap_Action.cxx b/fluid/Fd_Snap_Action.cxx
index f226ff156..ffd944cd8 100644
--- a/fluid/Fd_Snap_Action.cxx
+++ b/fluid/Fd_Snap_Action.cxx
@@ -30,7 +30,7 @@
 
 // TODO: warning if the user wants to change builtin layouts
 // TODO: move panel to global settings panel (move load & save to main pulldown, or to toolbox?)
-// INFO: how about a small tool box for quick preset selection and disabeling of individual snaps?
+// INFO: how about a small tool box for quick preset selection and disabling of individual snaps?
 
 void select_layout_suite_cb(Fl_Widget *, void *user_data);
 
diff --git a/fluid/Fd_Snap_Action.h b/fluid/Fd_Snap_Action.h
index 413e340f2..5b3731087 100644
--- a/fluid/Fd_Snap_Action.h
+++ b/fluid/Fd_Snap_Action.h
@@ -88,7 +88,7 @@ public:
   char *name_;                  ///< name of the suite
   char *menu_label;             ///< label text used in pulldown menu
   Fd_Layout_Preset *layout[3];  ///< presets for application, dialog, and toolbox windows
-  Fd_Tool_Store storage_;                 ///< storage location (see FD_STORE_INTERNAL, etc.)
+  Fd_Tool_Store storage_;       ///< storage location (see FD_STORE_INTERNAL, etc.)
   void write(Fl_Preferences &prefs);
   void read(Fl_Preferences &prefs);
   void write(Fd_Project_Writer*);
diff --git a/fluid/Fl_Button_Type.h b/fluid/Fl_Button_Type.h
index c731ce7e7..3eb4a3d1d 100644
--- a/fluid/Fl_Button_Type.h
+++ b/fluid/Fl_Button_Type.h
@@ -38,7 +38,6 @@ public:
   void write_properties(Fd_Project_Writer &f) FL_OVERRIDE;
   void read_property(Fd_Project_Reader &f, const char *) FL_OVERRIDE;
   void copy_properties() FL_OVERRIDE;
-
 };
 
 extern Fl_Button_Type Fl_Button_type;
diff --git a/fluid/Fl_Function_Type.cxx b/fluid/Fl_Function_Type.cxx
index ce6493911..f7a7f30d8 100644
--- a/fluid/Fl_Function_Type.cxx
+++ b/fluid/Fl_Function_Type.cxx
@@ -162,7 +162,7 @@ const char *_c_check(const char * & c, int type) {
  \note This function checks every conceivable line of code, which is not
     always wanted. It can't differentiate characters in comments, and the
     user may well intend to leave a curly bracket open
-    (i.e. namesapece { ... } ). We should make this option user selectable.
+    (i.e. namespace { ... } ). We should make this option user selectable.
  */
 const char *c_check(const char *c, int type) {
   return _c_check(c,type);
@@ -779,7 +779,7 @@ void Fl_CodeBlock_Type::write_properties(Fd_Project_Writer &f) {
 }
 
 /**
- Read the node specifc properties.
+ Read the node specific properties.
  */
 void Fl_CodeBlock_Type::read_property(Fd_Project_Reader &f, const char *c) {
   if (!strcmp(c,"after")) {
@@ -1441,7 +1441,7 @@ int Fl_DeclBlock_Type::is_public() const {return public_;}
 /**
  Create a new declaration block.
  \param[in] strategy add after current or as last child
- \return new Declaration Blocknode
+ \return new Declaration Block node
  */
 Fl_Type *Fl_DeclBlock_Type::make(Strategy strategy) {
   Fl_Type *p = Fl_Type::current;
diff --git a/fluid/Fl_Menu_Type.cxx b/fluid/Fl_Menu_Type.cxx
index ebc7a4653..b61a01031 100644
--- a/fluid/Fl_Menu_Type.cxx
+++ b/fluid/Fl_Menu_Type.cxx
@@ -381,14 +381,14 @@ void Fl_Menu_Item_Type::write_item(Fd_Code_Writer& f) {
   f.write_c(" {");
   if (label() && label()[0])
     switch (g_project.i18n_type) {
-      case 1:
+      case FD_I18N_GNU:
         // we will call i18n when the menu is instantiated for the first time
         f.write_c("%s(", g_project.i18n_gnu_static_function.c_str());
         f.write_cstring(label());
         f.write_c(")");
         break;
-      case 2:
-        // fall through: strings can't be translated before a catalog is choosen
+      case FD_I18N_POSIX:
+        // fall through: strings can't be translated before a catalog is chosen
       default:
         f.write_cstring(label());
     }
@@ -486,15 +486,16 @@ void Fl_Menu_Item_Type::write_code1(Fd_Code_Writer& f) {
       f.write_c("%sml->labela = (char*)", f.indent());
       image->write_inline(f);
       f.write_c(";\n");
-      if (g_project.i18n_type==0) {
+      if (g_project.i18n_type==FD_I18N_NONE) {
         f.write_c("%sml->labelb = o->label();\n", f.indent());
-      } else if (g_project.i18n_type==1) {
+      } else if (g_project.i18n_type==FD_I18N_GNU) {
         f.write_c("%sml->labelb = %s(o->label());\n",
                 f.indent(), g_project.i18n_gnu_function.c_str());
-      } else if (g_project.i18n_type==2) {
+      } else if (g_project.i18n_type==FD_I18N_POSIX) {
         f.write_c("%sml->labelb = catgets(%s,%s,i+%d,o->label());\n",
-                f.indent(), g_project.i18n_pos_file[0] ? g_project.i18n_pos_file.c_str() : "_catalog",
-                g_project.i18n_pos_set.c_str(), msgnum());
+                  f.indent(), 
+                  g_project.i18n_pos_file.empty() ? "_catalog" : g_project.i18n_pos_file.c_str(),
+                  g_project.i18n_pos_set.c_str(), msgnum());
       }
       f.write_c("%sml->typea = FL_IMAGE_LABEL;\n", f.indent());
       f.write_c("%sml->typeb = FL_NORMAL_LABEL;\n", f.indent());
@@ -510,13 +511,14 @@ void Fl_Menu_Item_Type::write_code1(Fd_Code_Writer& f) {
     } else if (   t==FL_NORMAL_LABEL   || t==FL_SHADOW_LABEL
                || t==FL_ENGRAVED_LABEL || t==FL_EMBOSSED_LABEL) {
       start_menu_initialiser(f, menuItemInitialized, mname, i);
-      if (g_project.i18n_type==1) {
+      if (g_project.i18n_type==FD_I18N_GNU) {
         f.write_c("%so->label(%s(o->label()));\n",
                 f.indent(), g_project.i18n_gnu_function.c_str());
-      } else if (g_project.i18n_type==2) {
+      } else if (g_project.i18n_type==FD_I18N_POSIX) {
         f.write_c("%so->label(catgets(%s,%s,i+%d,o->label()));\n",
-                f.indent(), g_project.i18n_pos_file[0] ? g_project.i18n_pos_file.c_str() : "_catalog",
-                g_project.i18n_pos_set.c_str(), msgnum());
+                  f.indent(),
+                  g_project.i18n_pos_file.empty() ? "_catalog" : g_project.i18n_pos_file.c_str(),
+                  g_project.i18n_pos_set.c_str(), msgnum());
       }
     }
   }
diff --git a/fluid/Fl_Type.h b/fluid/Fl_Type.h
index d96f4db99..39a9bb30b 100644
--- a/fluid/Fl_Type.h
+++ b/fluid/Fl_Type.h
@@ -1,7 +1,7 @@
 //
 // Widget type header file for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2023 by Bill Spitzak and others.
+// Copyright 1998-2024 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -130,7 +130,7 @@ public: // things that should not be public:
   Fl_Type *parent;
   /** This type is rendered "selected" in the tree browser. */
   char new_selected; // browser highlight
-  /** Backup storage for selection if an error accured during some operation
+  /** Backup storage for selection if an error occurred during some operation
    (see `haderror`). It seems that this is often confused with new_selected
    which seems to hold the true and visible selection state. */
   char selected; // copied here by selection_changed()
@@ -225,9 +225,9 @@ public:
   void write_comment_inline_c(Fd_Code_Writer& f, const char *ind=0L); // write the commentary text
 
   // live mode
-  virtual Fl_Widget *enter_live_mode(int top=0); // build wdgets needed for live mode
+  virtual Fl_Widget *enter_live_mode(int top=0); // build widgets needed for live mode
   virtual void leave_live_mode(); // free allocated resources
-  virtual void copy_properties(); // copy properties from this type into a potetial live object
+  virtual void copy_properties(); // copy properties from this type into a potential live object
 
   // get message number for I18N
   int msgnum();
diff --git a/fluid/Fl_Widget_Type.cxx b/fluid/Fl_Widget_Type.cxx
index ac93aeeff..d223fba86 100644
--- a/fluid/Fl_Widget_Type.cxx
+++ b/fluid/Fl_Widget_Type.cxx
@@ -2997,17 +2997,18 @@ void Fl_Widget_Type::write_code1(Fd_Code_Writer& f) {
   if (label() && *label()) {
     f.write_c(", ");
     switch (g_project.i18n_type) {
-    case 0 : /* None */
+    case FD_I18N_NONE : /* None */
         f.write_cstring(label());
         break;
-    case 1 : /* GNU gettext */
+    case FD_I18N_GNU : /* GNU gettext */
         f.write_c("%s(", g_project.i18n_gnu_function.c_str());
         f.write_cstring(label());
         f.write_c(")");
         break;
-    case 2 : /* POSIX catgets */
-        f.write_c("catgets(%s,%s,%d,", g_project.i18n_pos_file[0] ? g_project.i18n_pos_file.c_str() : "_catalog",
-                g_project.i18n_pos_set.c_str(), msgnum());
+    case FD_I18N_POSIX : /* POSIX catgets */
+        f.write_c("catgets(%s,%s,%d,", 
+                  g_project.i18n_pos_file.empty() ? "_catalog" : g_project.i18n_pos_file.c_str(),
+                  g_project.i18n_pos_set.c_str(), msgnum());
         f.write_cstring(label());
         f.write_c(")");
         break;
@@ -3070,17 +3071,19 @@ void Fl_Widget_Type::write_widget_code(Fd_Code_Writer& f) {
   if (tooltip() && *tooltip()) {
     f.write_c("%s%s->tooltip(",f.indent(), var);
     switch (g_project.i18n_type) {
-    case 0 : /* None */
+    case FD_I18N_NONE : /* None */
         f.write_cstring(tooltip());
         break;
-    case 1 : /* GNU gettext */
+    case FD_I18N_GNU : /* GNU gettext */
         f.write_c("%s(", g_project.i18n_gnu_function.c_str());
         f.write_cstring(tooltip());
         f.write_c(")");
         break;
-    case 2 : /* POSIX catgets */
-        f.write_c("catgets(%s,%s,%d,", g_project.i18n_pos_file[0] ? g_project.i18n_pos_file.c_str() : "_catalog",
-                g_project.i18n_pos_set.c_str(), msgnum() + 1);
+    case FD_I18N_POSIX : /* POSIX catgets */
+        f.write_c("catgets(%s,%s,%d,",
+                  g_project.i18n_pos_file.empty() ? "_catalog" : g_project.i18n_pos_file.c_str(),
+                  g_project.i18n_pos_set.c_str(), 
+                  msgnum() + 1);
         f.write_cstring(tooltip());
         f.write_c(")");
         break;
diff --git a/fluid/Fl_Widget_Type.h b/fluid/Fl_Widget_Type.h
index bcbafe4a1..b1773a501 100644
--- a/fluid/Fl_Widget_Type.h
+++ b/fluid/Fl_Widget_Type.h
@@ -57,7 +57,7 @@ protected:
   /// This variable is set for visible windows in batch mode.
   /// We can't open a window in batch mode, even if we want the "visible" flags
   /// set, so we need a second place to store this information while also
-  /// disabeling the output of the "hide" property by the Widget Type.
+  /// disabling the output of the "hide" property by the Widget Type.
   uchar override_visible_;
 
   void write_static(Fd_Code_Writer& f) FL_OVERRIDE;
diff --git a/fluid/Fl_Window_Type.cxx b/fluid/Fl_Window_Type.cxx
index db9ec34ba..bc848ed75 100644
--- a/fluid/Fl_Window_Type.cxx
+++ b/fluid/Fl_Window_Type.cxx
@@ -73,19 +73,19 @@ void i18n_type_cb(Fl_Choice *c, void *v) {
     c->value(g_project.i18n_type);
   } else {
     undo_checkpoint();
-    g_project.i18n_type = c->value();
+    g_project.i18n_type = static_cast<Fd_I18n_Type>(c->value());
     set_modflag(1);
   }
   switch (g_project.i18n_type) {
-  case 0 : /* None */
+  case FD_I18N_NONE : /* None */
       i18n_gnu_group->hide();
       i18n_posix_group->hide();
       break;
-  case 1 : /* GNU gettext */
+  case FD_I18N_GNU : /* GNU gettext */
       i18n_gnu_group->show();
       i18n_posix_group->hide();
       break;
-  case 2 : /* POSIX cat */
+  case FD_I18N_POSIX : /* POSIX cat */
       i18n_gnu_group->hide();
       i18n_posix_group->show();
       break;
diff --git a/fluid/Fl_Window_Type.h b/fluid/Fl_Window_Type.h
index 56abd630f..779c7b787 100644
--- a/fluid/Fl_Window_Type.h
+++ b/fluid/Fl_Window_Type.h
@@ -1,5 +1,5 @@
 //
-// Widget type header file for the Fast Light Tool Kit (FLTK).
+// Window type header file for the Fast Light Tool Kit (FLTK).
 //
 // Type for creating all subclasses of Fl_Widget
 // This should have the widget pointer in it, but it is still in the
diff --git a/fluid/code.cxx b/fluid/code.cxx
index d220ab712..eef2aac47 100644
--- a/fluid/code.cxx
+++ b/fluid/code.cxx
@@ -94,7 +94,7 @@ int write_strings(const Fl_String &filename) {
   if (!fp) return 1;
 
   switch (g_project.i18n_type) {
-    case 0 : /* None, just put static text out */
+    case FD_I18N_NONE : /* None, just put static text out */
       fprintf(fp, "# generated by Fast Light User Interface Designer (fluid) version %.4f\n",
               FL_VERSION);
       for (p = Fl_Type::first; p; p = p->next) {
@@ -113,7 +113,7 @@ int write_strings(const Fl_String &filename) {
         }
       }
       break;
-    case 1 : /* GNU gettext, put a .po file out */
+    case FD_I18N_GNU : /* GNU gettext, put a .po file out */
       fprintf(fp, "# generated by Fast Light User Interface Designer (fluid) version %.4f\n",
               FL_VERSION);
       for (p = Fl_Type::first; p; p = p->next) {
@@ -142,7 +142,7 @@ int write_strings(const Fl_String &filename) {
         }
       }
       break;
-    case 2 : /* POSIX catgets, put a .msg file out */
+    case FD_I18N_POSIX : /* POSIX catgets, put a .msg file out */
       fprintf(fp, "$ generated by Fast Light User Interface Designer (fluid) version %.4f\n",
               FL_VERSION);
       fprintf(fp, "$set %s\n", g_project.i18n_pos_set.c_str());
@@ -844,7 +844,7 @@ int Fd_Code_Writer::write_code(const char *s, const char *t, bool to_sourceview)
     }
   }
   Fl_String loc_include, loc_conditional;
-  if (g_project.i18n_type==1) {
+  if (g_project.i18n_type==FD_I18N_GNU) {
     loc_include = g_project.i18n_gnu_include;
     loc_conditional = g_project.i18n_gnu_conditional;
   } else {
@@ -861,7 +861,7 @@ int Fd_Code_Writer::write_code(const char *s, const char *t, bool to_sourceview)
       write_c("#%sinclude \"%s\"\n", indent(), loc_include.c_str());
     else
       write_c("#%sinclude %s\n", indent(), loc_include.c_str());
-    if (g_project.i18n_type == 2) {
+    if (g_project.i18n_type == FD_I18N_POSIX) {
       if (!g_project.i18n_pos_file.empty()) {
         write_c("extern nl_catd %s;\n", g_project.i18n_pos_file.c_str());
       } else {
@@ -873,14 +873,14 @@ int Fd_Code_Writer::write_code(const char *s, const char *t, bool to_sourceview)
     }
     if (conditional) {
       write_c("#else\n");
-      if (g_project.i18n_type == 1) {
+      if (g_project.i18n_type == FD_I18N_GNU) {
         if (!g_project.i18n_gnu_function.empty()) {
           write_c("#%sifndef %s\n", indent(), g_project.i18n_gnu_function.c_str());
           write_c("#%sdefine %s(text) text\n", indent_plus(1), g_project.i18n_gnu_function.c_str());
           write_c("#%sendif\n", indent());
         }
       }
-      if (g_project.i18n_type == 2) {
+      if (g_project.i18n_type == FD_I18N_POSIX) {
         write_c("#%sifndef catgets\n", indent());
         write_c("#%sdefine catgets(catalog, set, msgid, text) text\n", indent_plus(1));
         write_c("#%sendif\n", indent());
@@ -888,7 +888,7 @@ int Fd_Code_Writer::write_code(const char *s, const char *t, bool to_sourceview)
       indentation--;
       write_c("#endif\n");
     }
-    if (g_project.i18n_type == 1 && g_project.i18n_gnu_static_function[0]) {
+    if (g_project.i18n_type == FD_I18N_GNU && g_project.i18n_gnu_static_function[0]) {
       write_c("#ifndef %s\n", g_project.i18n_gnu_static_function.c_str());
       write_c("#%sdefine %s(text) text\n", indent_plus(1), g_project.i18n_gnu_static_function.c_str());
       write_c("#endif\n");
diff --git a/fluid/file.cxx b/fluid/file.cxx
index b20191291..a054a34cb 100644
--- a/fluid/file.cxx
+++ b/fluid/file.cxx
@@ -283,7 +283,7 @@ Fl_Type *Fd_Project_Reader::read_children(Fl_Type *p, int merge, Strategy strate
         goto CONTINUE;
       }
       if (!strcmp(c,"i18n_type")) {
-        g_project.i18n_type = atoi(read_word());
+        g_project.i18n_type = static_cast<Fd_I18n_Type>(atoi(read_word()));
         goto CONTINUE;
       }
       if (!strcmp(c,"i18n_gnu_function")) {
@@ -303,16 +303,16 @@ Fl_Type *Fd_Project_Reader::read_children(Fl_Type *p, int merge, Strategy strate
         goto CONTINUE;
       }
       if (!strcmp(c,"i18n_include")) {
-        if (g_project.i18n_type == 1)
+        if (g_project.i18n_type == FD_I18N_GNU)
           g_project.i18n_gnu_include = read_word();
-        else if (g_project.i18n_type == 2)
+        else if (g_project.i18n_type == FD_I18N_POSIX)
           g_project.i18n_pos_include = read_word();
         goto CONTINUE;
       }
       if (!strcmp(c,"i18n_conditional")) {
-        if (g_project.i18n_type == 1)
+        if (g_project.i18n_type == FD_I18N_GNU)
           g_project.i18n_gnu_conditional = read_word();
-        else if (g_project.i18n_type == 2)
+        else if (g_project.i18n_type == FD_I18N_POSIX)
           g_project.i18n_pos_conditional = read_word();
         goto CONTINUE;
       }
@@ -847,13 +847,15 @@ int Fd_Project_Writer::write_project(const char *filename, int selected_only, bo
   if (g_project.i18n_type) {
     write_string("\ni18n_type %d", g_project.i18n_type);
     switch (g_project.i18n_type) {
-      case 1 : /* GNU gettext */
+      case FD_I18N_NONE:
+        break;
+      case FD_I18N_GNU : /* GNU gettext */
         write_string("\ni18n_include"); write_word(g_project.i18n_gnu_include.c_str());
         write_string("\ni18n_conditional"); write_word(g_project.i18n_gnu_conditional.c_str());
         write_string("\ni18n_gnu_function"); write_word(g_project.i18n_gnu_function.c_str());
         write_string("\ni18n_gnu_static_function"); write_word(g_project.i18n_gnu_static_function.c_str());
         break;
-      case 2 : /* POSIX catgets */
+      case FD_I18N_POSIX : /* POSIX catgets */
         write_string("\ni18n_include"); write_word(g_project.i18n_pos_include.c_str());
         write_string("\ni18n_conditional"); write_word(g_project.i18n_pos_conditional.c_str());
         if (!g_project.i18n_pos_file.empty()) {
diff --git a/fluid/fluid.cxx b/fluid/fluid.cxx
index 3b05b5708..42fe3d218 100644
--- a/fluid/fluid.cxx
+++ b/fluid/fluid.cxx
@@ -1,7 +1,7 @@
 //
 // FLUID main entry for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2023 by Bill Spitzak and others.
+// Copyright 1998-2024 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -67,10 +67,13 @@ extern "C"
 // Globals..
 //
 
-/// Fluid-wide help dialog.
-static Fl_Help_Dialog *help_dialog = 0;
+/// FLUID-wide help dialog.
+static Fl_Help_Dialog *help_dialog = NULL;
 
+/// Main app window menu bar.
 Fl_Menu_Bar *main_menubar = NULL;
+
+/// Main app window.
 Fl_Window *main_window;
 
 /// Fluid application preferences, always accessible, will be flushed when app closes.
@@ -115,10 +118,10 @@ int reading_file = 0;
 // File history info...
 
 /// Stores the absolute filename of the last 10 design files, saved in app preferences.
-char    absolute_history[10][FL_PATH_MAX];
+char absolute_history[10][FL_PATH_MAX];
 
 /// This list of filenames is computed from \c absolute_history and displayed in the main menu.
-char    relative_history[10][FL_PATH_MAX];
+char relative_history[10][FL_PATH_MAX];
 
 /// Menuitem to save a .fl design file, will be deactivated if the design is unchanged.
 Fl_Menu_Item *save_item = NULL;
@@ -143,7 +146,7 @@ Fl_Menu_Item *restricted_item = NULL;
 
 ////////////////////////////////////////////////////////////////
 
-/// Filename of the current .fl design file
+/// Filename of the current .fl project file
 static const char *filename = NULL;
 
 /// Set if the current design has been modified compared to the associated .fl design file.
@@ -172,105 +175,23 @@ int compile_strings = 0;        // fluid -cs
 /// Set, if Fluid runs in batch mode, and no user interface is activated.
 int batch_mode = 0;             // if set (-c, -u) don't open display
 
-/// command line arguments override settings in the project file
+/// command line arguments that overrides the generate code file extension or name
 Fl_String g_code_filename_arg;
+
+/// command line arguments that overrides the generate header file extension or name
 Fl_String g_header_filename_arg;
+
+/// current directory path at application launch
 Fl_String g_launch_path;
 
+/// path to store temporary files during app run
+/// \see tmpdir_create_called
 Fl_String tmpdir_path;
+
+/// true if the temporary file path was already created
+/// \see tmpdir_path
 bool tmpdir_create_called = false;
 
-/** \var int Fluid_Project::header_file_set
- If set, command line overrides header file name in .fl file.
- */
-
-/** \var int Fluid_Project::code_file_set
- If set, command line overrides source code file name in .fl file.
- */
-
-/** \var int Fluid_Project::header_file_name
- Hold the default extension for header files, or the entire filename if set via command line.
- */
-
-/** \var int Fluid_Project::code_file_name
- Hold the default extension for source code  files, or the entire filename if set via command line.
- */
-
-/** \var int Fluid_Project::i18n_type
- Saved in the .fl design file.
- \todo document me
- */
-
-/** \var int Fluid_Project::i18n_gnu_include
- Include file for GNU i18n, writes an #include statement into the
- source file.
-
- This is usually `<libintl.h>` or `"gettext.h"` for GNU gettext.
-
- Fluid accepts filenames in quotes or in \< and \>. If neither is found,
- double quotes are added.
- If this value is empty, no include statement will be generated.
-
- Saved in the .fl design file if GNU i18n is selected.
- */
-
-/** \var int Fluid_Project::i18n_pos_include
- Include file for Posix i18n, write a #include statement into the
- source file.
-
- This is usually `<nl_types.h>` for Posix catgets.
-
- Fluid accepts filenames in quotes or in \< and \>. If neither is found,
- double quotes are added.
- If this value is empty, no include statement will be generated.
-
- Saved in the .fl design file.
- */
-
-/** \var int Fluid_Project::i18n_gnu_conditional
- Saved in the .fl design file.
- \todo document me
- */
-
-/** \var int Fluid_Project::i18n_pos_conditional
- Saved in the .fl design file.
- \todo document me
- */
-
-/** \var int Fluid_Project::i18n_gnu_function
- For the gettext/intl.h options, this is the function that translates text
- at runtime.
-
- This is usually "gettext" or "_".
- This should not be empty.
- Saved in the .fl design file.
- */
-
-/** \var int Fluid_Project::i18n_gnu_static_function
- For the gettext/intl.h options, this is the function that marks the
- translation of text at initialisation time.
-
- This is usually "gettext_noop" or "N_".
- This should not be empty.
- Fluid will translate static text (usually in menu items) later when used
- for the first time.
-
- Saved in the .fl design file.
- */
-
-/** \var int Fluid_Project::i18n_pos_file
- Saved in the .fl design file.
- \todo document me
- */
-
-/** \var int Fluid_Project::i18n_pos_set
- Saved in the .fl design file.
- \todo document me
- */
-
-/** \var int Fluid_Project::basename
- \todo document me
- */
 
 /// Offset in pixels when adding widgets from an .fl file.
 int pasteoffset = 0;
@@ -280,10 +201,14 @@ static int ipasteoffset = 0;
 
 // ---- project settings
 
+/// The current project, possibly a new, empty roject
 Fluid_Project g_project;
 
+/**
+ Initialize a new project.
+ */
 Fluid_Project::Fluid_Project() :
-  i18n_type(0),
+  i18n_type(FD_I18N_NONE),
   include_H_from_C(1),
   use_FL_COMMAND(0),
   utf8_in_src(0),
@@ -295,12 +220,19 @@ Fluid_Project::Fluid_Project() :
   code_file_name(".cxx")
 { }
 
+/**
+ Clear all project resources.
+ Not implemented.
+ */
 Fluid_Project::~Fluid_Project() {
 }
 
+/**
+ Reset all project setting to create a new empty project.
+ */
 void Fluid_Project::reset() {
   ::delete_all();
-  i18n_type = 0;
+  i18n_type = FD_I18N_NONE;
 
   i18n_gnu_include = "<libintl.h>";
   i18n_gnu_conditional = "";
@@ -323,6 +255,9 @@ void Fluid_Project::reset() {
   write_mergeback_data = 0;
 }
 
+/**
+ Tell the project and i18n tab of the settings dialog to refresh themselves.
+ */
 void Fluid_Project::update_settings_dialog() {
   if (settings_window) {
     w_settings_project_tab->do_callback(w_settings_project_tab, LOAD);
@@ -330,7 +265,11 @@ void Fluid_Project::update_settings_dialog() {
   }
 }
 
-// make sure that a path name ends with a forward slash
+/**
+ Make sure that a path name ends with a forward slash.
+ \param[in] str directory or path name
+ \return a new string, ending with a '/'
+ */
 static Fl_String end_with_slash(const Fl_String &str) {
   char last = str[str.size()-1];
   if (last !='/' && last != '\\')
@@ -339,7 +278,8 @@ static Fl_String end_with_slash(const Fl_String &str) {
     return str;
 }
 
-/** Generate a path to a directory for temporary data storage.
+/** 
+ Generate a path to a directory for temporary data storage.
  The path is stored in g_tmpdir.
  */
 static void create_tmpdir() {
@@ -396,11 +336,18 @@ static void create_tmpdir() {
     fl_make_path(path.c_str());
     if (fl_access(path.c_str(), 6) == 0) tmpdir_path = path;
   }
-  if (tmpdir_path.empty())
-    fl_alert("Can't create directory for temporary data storage.");
+  if (tmpdir_path.empty()) {
+    if (batch_mode) {
+      fprintf(stderr, "ERROR: Can't create directory for temporary data storage.\n");
+    } else {
+      fl_alert("Can't create directory for temporary data storage.");
+    }
+  }
 }
 
-/** Delete the temporary directory that was created in set_tmpdir. */
+/** 
+ Delete the temporary directory that was created in set_tmpdir.
+ */
 static void delete_tmpdir() {
   // was a temporary directory created
   if (!tmpdir_create_called)
@@ -421,7 +368,11 @@ static void delete_tmpdir() {
 
   // then delete the directory itself
   if (fl_rmdir(tmpdir_path.c_str()) < 0) {
-    fl_alert("WARNING: Can't delete tmpdir '%s': %s", tmpdir_path.c_str(), strerror(errno));
+    if (batch_mode) {
+      fprintf(stderr, "WARNING: Can't delete tmpdir '%s': %s", tmpdir_path.c_str(), strerror(errno));
+    } else {
+      fl_alert("WARNING: Can't delete tmpdir '%s': %s", tmpdir_path.c_str(), strerror(errno));
+    }
   }
 }
 
@@ -429,7 +380,7 @@ static void delete_tmpdir() {
  Return the path to a temporary directory for this instance of FLUID.
  Fluid will do its best to clear and delete this directory when exiting.
  \return the path to the temporary directory, ending in a '/', or and empty
-      string is no directory could be created.
+      string if no directory could be created.
  */
 const Fl_String &get_tmpdir() {
   if (!tmpdir_create_called)
@@ -468,7 +419,13 @@ bool confirm_project_clear() {
 // ----
 
 extern Fl_Window *the_panel;
-// make sure that a currently changed text widgets propagates its contents
+
+/**
+ Ensure that text widgets in the widget panel propagates apply current changes.
+ By temporarily clearing the text focus, all text widgets with changed text
+ will unfocus and call their respective callbacks, propagating those changes to
+ their data set.
+ */
 void flush_text_widgets() {
   if (Fl::focus() && (Fl::focus()->top_window() == the_panel)) {
     Fl_Widget *old_focus = Fl::focus();
@@ -476,6 +433,7 @@ void flush_text_widgets() {
     Fl::focus(old_focus);
   }
 }
+
 // ----
 
 /**
@@ -814,8 +772,13 @@ void revert_cb(Fl_Widget *,void *) {
  */
 void exit_cb(Fl_Widget *,void *) {
   if (shell_command_running()) {
-    fl_alert("Previous shell command still running!");
-    return;
+    int choice = fl_choice("Previous shell command still running!",
+                           "Cancel",
+                           "Exit",
+                           NULL);
+    if (choice == 0) { // user chose to cancel the exit operation
+      return;
+    }
   }
 
   flush_text_widgets();
@@ -874,6 +837,8 @@ void exit_cb(Fl_Widget *,void *) {
  If the current project was modified, FLUID will give the user the opportunity
  to save the old project first.
 
+ \param[in] user_must_confirm if set, a confimation dialog is presented to the
+    user before resetting the project.
  \return false if the operation was canceled
  */
 bool new_project(bool user_must_confirm = true) {
@@ -1122,6 +1087,7 @@ void apple_open_cb(const char *c) {
 
 /**
  Get the absolute path of the project file, for example `/Users/matt/dev/`.
+ \return the path ending in '/'
  */
 Fl_String Fluid_Project::projectfile_path() const {
   return end_with_slash(fl_filename_absolute(fl_filename_path(filename), g_launch_path));
@@ -1129,6 +1095,7 @@ Fl_String Fluid_Project::projectfile_path() const {
 
 /**
  Get the project file name including extension, for example `test.fl`.
+ \return the file name without path
  */
 Fl_String Fluid_Project::projectfile_name() const {
   return fl_filename_name(filename);
@@ -1136,6 +1103,7 @@ Fl_String Fluid_Project::projectfile_name() const {
 
 /**
  Get the absolute path of the generated C++ code file, for example `/Users/matt/dev/src/`.
+ \return the path ending in '/'
  */
 Fl_String Fluid_Project::codefile_path() const {
   Fl_String path = fl_filename_path(code_file_name);
@@ -1147,6 +1115,7 @@ Fl_String Fluid_Project::codefile_path() const {
 
 /**
  Get the generated C++ code file name including extension, for example `test.cxx`.
+ \return the file name without path
  */
 Fl_String Fluid_Project::codefile_name() const {
   Fl_String name = fl_filename_name(code_file_name);
@@ -1161,6 +1130,7 @@ Fl_String Fluid_Project::codefile_name() const {
 
 /**
  Get the absolute path of the generated C++ header file, for example `/Users/matt/dev/src/`.
+ \return the path ending in '/'
  */
 Fl_String Fluid_Project::headerfile_path() const {
   Fl_String path = fl_filename_path(header_file_name);
@@ -1172,6 +1142,7 @@ Fl_String Fluid_Project::headerfile_path() const {
 
 /**
  Get the generated C++ header file name including extension, for example `test.cxx`.
+ \return the file name without path
  */
 Fl_String Fluid_Project::headerfile_name() const {
   Fl_String name = fl_filename_name(header_file_name);
@@ -1190,33 +1161,35 @@ Fl_String Fluid_Project::headerfile_name() const {
  with the source and header file, historically, the text is always saved with
  the project file in interactive mode, and in the FLUID launch directory in
  batch mode.
+ \return the path ending in '/'
  */
 Fl_String Fluid_Project::stringsfile_path() const {
   if (batch_mode)
-    return end_with_slash(g_launch_path);
+    return g_launch_path;
   else
     return projectfile_path();
 }
 
 /**
  Get the generated i18n text file name including extension, for example `test.po`.
+ \return the file name without path
  */
 Fl_String Fluid_Project::stringsfile_name() const {
   switch (i18n_type) {
     default: return fl_filename_setext(fl_filename_name(filename), ".txt");
-    case 1: return fl_filename_setext(fl_filename_name(filename), ".po");
-    case 2: return fl_filename_setext(fl_filename_name(filename), ".msg");
+    case FD_I18N_GNU: return fl_filename_setext(fl_filename_name(filename), ".po");
+    case FD_I18N_POSIX: return fl_filename_setext(fl_filename_name(filename), ".msg");
   }
 }
 
 /**
  Get the name of the project file without the filename extension.
+ \return the file name without path or extension
  */
 Fl_String Fluid_Project::basename() const {
   return fl_filename_setext(fl_filename_name(filename), "");
 }
 
-
 /**
  Generate the C++ source and header filenames and write those files.
 
@@ -1234,6 +1207,7 @@ Fl_String Fluid_Project::basename() const {
  In interactive mode, it will pop up an error message, or, if the user
  hasn't disabled that, pop up a confirmation message.
 
+ \param[in] dont_show_completion_dialog don't show the completion dialog
  \return 1 if the operation failed, 0 if it succeeded
  */
 int write_code_files(bool dont_show_completion_dialog)
@@ -1670,7 +1644,7 @@ static void menu_file_open_history_cb(Fl_Widget *, void *v) { open_project_file(
  \c New_Menu creates new widgets and is explained in detail in another location.
 
  \see New_Menu
- \todo This menu need some major modernisation. Menus are too long and their
+ \todo This menu needs some major modernization. Menus are too long and their
     sorting is not always obvious.
  \todo Shortcuts are all over the place (Alt, Ctrl, Command, Shift-Ctrl,
     function keys), and there should be a help page listing all shortcuts.
@@ -1772,6 +1746,8 @@ Fl_Menu_Item Main_Menu[] = {
  This callback is triggered by changing the scheme in the
  Fl_Scheme_Choice widget (\p Edit/GUI Settings).
 
+ \param[in] choice the calling widget
+
  \see init_scheme() for choice values and backwards compatibility
  */
 void scheme_cb(Fl_Scheme_Choice *choice, void *) {
@@ -1860,10 +1836,16 @@ void toggle_widgetbin_cb(Fl_Widget *, void *) {
   }
 }
 
+/**
+ Show or hide the code preview window.
+ */
 void toggle_sourceview_cb(Fl_Double_Window *, void *) {
   sourceview_toggle_visibility();
 }
 
+/**
+ Show or hide the code preview window, button callback.
+ */
 void toggle_sourceview_b_cb(Fl_Button*, void *) {
   sourceview_toggle_visibility();
 }
diff --git a/fluid/fluid.h b/fluid/fluid.h
index d305598ac..b71baaeb7 100644
--- a/fluid/fluid.h
+++ b/fluid/fluid.h
@@ -1,7 +1,7 @@
 //
 // FLUID main entry for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2023 by Bill Spitzak and others.
+// Copyright 1998-2024 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -100,6 +100,18 @@ extern Fl_String g_launch_path;
 
 // ---- project class declaration
 
+/**
+ Enumeration of available internationalization types.
+ */
+typedef enum {
+  FD_I18N_NONE = 0, ///< No i18n, all strings are litearals
+  FD_I18N_GNU,      ///< GNU gettext internationalization
+  FD_I18N_POSIX     ///< Posix catgets internationalization
+} Fd_I18n_Type;
+
+/**
+ Data and settings for a FLUID project file.
+ */
 class Fluid_Project {
 public:
   Fluid_Project();
@@ -117,25 +129,46 @@ public:
   Fl_String stringsfile_name() const;
   Fl_String basename() const;
 
-  int i18n_type;
+  /// One of the available internationalization types.
+  Fd_I18n_Type i18n_type;
+  /// Include file for GNU i18n, writes an #include statement into the source
+  /// file. This is usually `<libintl.h>` or `"gettext.h"` for GNU gettext.
   Fl_String i18n_gnu_include;
+  // Optional name of a macro for conditional i18n compilation.
   Fl_String i18n_gnu_conditional;
+  /// For the gettext/intl.h options, this is the function that translates text
+  /// at runtime. This is usually "gettext" or "_".
   Fl_String i18n_gnu_function;
+  /// For the gettext/intl.h options, this is the function that marks the translation
+  /// of text at initialisation time. This is usually "gettext_noop" or "N_".
   Fl_String i18n_gnu_static_function;
 
+  /// Include file for Posix i18n, write a #include statement into the source
+  /// file. This is usually `<nl_types.h>` for Posix catgets.
   Fl_String i18n_pos_include;
+  // Optional name of a macro for conditional i18n compilation.
   Fl_String i18n_pos_conditional;
+  /// Name of the nl_catd database
   Fl_String i18n_pos_file;
+  /// Message set ID for the catalog.
   Fl_String i18n_pos_set;
 
+  /// If set, generate code to include the header file form the c++ file
   int include_H_from_C;
+  /// If set, handle keyboard shortcut Ctrl on macOS using Cmd instead
   int use_FL_COMMAND;
+  /// Clear if UTF-8 characters in statics texts are written as escape sequences
   int utf8_in_src;
+  /// If set, <FL/Fl.H> will not be included from the header code before anything else
   int avoid_early_includes;
+  /// If set, command line overrides header file name in .fl file.
   int header_file_set;
+  ///  If set, command line overrides source code file name in .fl file.
   int code_file_set;
   int write_mergeback_data;
+  /// Hold the default extension for header files, or the entire filename if set via command line.
   Fl_String header_file_name;
+  /// Hold the default extension for source code  files, or the entire filename if set via command line.
   Fl_String code_file_name;
 };