Document Fl_Multiline_Output keynav and caret cursor

FL/Fl_Multiline_Output.H

@@ -34,6 +34,15 @@
   and need scrollbars, or full color control of characters,
   then use Fl_Text_Display. If you want to display HTML text,
   use Fl_Help_View.
+
+  A caret cursor (^) shows the keyboard navigation mark
+  for keyboard selection of the output text, e.g. Arrow Keys
+  to move the cursor, Shift + Arrow Keys to create a text
+  selection, and '^C' to copy the selected text to the paste buffer.
+  The caret cursor can be disabled by disabling the widget's
+  "visible focus" using clear_visible_focus(), inherited from the
+  Fl_Widget base class. Doing this also disables the widget's
+  keyboard navigation.
 */
 class FL_EXPORT Fl_Multiline_Output : public Fl_Output {
 public:

src/Fl_Input_.cxx

@@ -371,6 +371,7 @@ void Fl_Input_::drawtext(int X, int Y, int W, int H) {
       // cursor position may need to be recomputed (see STR #2486)
       curx = int(expandpos(p, value()+position(), buf, 0)+.5);
       if (readonly()) {
+        // Draw '^' caret cursor
         fl_line((int)(xpos+curx-2.5f), Y+ypos+height-1,
                 (int)(xpos+curx+0.5f), Y+ypos+height-4,
                 (int)(xpos+curx+3.5f), Y+ypos+height-1);