bug#11509: 24.0.97; hl-line overlay priority; column highlighting; crosshairs

[Drew Adams]

1. hl-line.el uses an overlay but does not give users an easy way to set
its priority.  Depending on the use of hl-line (see below), it can be
useful/important to have its overlay appear on top of other overlays
that might exist.
 

2. Consider integrating the features of these small add-on libraries:
 
vline.el - http://www.emacswiki.org/cgi-bin/wiki/vline.el
           http://bitbucket.org/buzztaiki/elisp/src/tip/vline.el
           author: Taiki SUGAWARA <buzz.taiki@gmail.com>
 
hl-line+.el -
           http://www.emacswiki.org/cgi-bin/wiki/hl-line+.el
           (requires hl-line.el)
 
col-highlight.el -
           http://www.emacswiki.org/cgi-bin/wiki/col-highlight.el
           (requires vline.el)
 
crosshairs.el -
           http://www.emacswiki.org/cgi-bin/wiki/crosshairs.el
           (requires hl-line+.el and col-highlight.el)
 
The last three are my code.  For vline.el you would need to check
whether Sugawara san has signed or will sign papars.  vline.el is needed
for the other code (except for hl-line+.el).
 

3. What they do:
 
vline.el - column highlighting
 
hl-line+.el -
           Alternative hl-line behaviors: turn it on only when Emacs
           is idle, or turn it on for only a few seconds (flash).
 
col-highlight.el -
           Alternative column highlighting behaviors: idle or flash
           (see previous).
 
crosshairs.el -
           Puts line & column highlighting together, to provide
           crosshairs for easily locating point.
 
Suggested keybinding: `crosshairs-mode' to `C-+'.
 

4. hl-line+.el and col-highlight.el allow a user to set the overlay
priority.  This can be especially important for crosshairs
highlighting and perhaps for vertical highlighting as well.  Whether you
want such highlighting to appear "on top" depends on what you use the
highlighting for.  It generally makes sense to show crosshairs on top.
 
5. I can provide a patch if you want to do this.  What is patched and
how would depend on what is decided.
 
IMO, it is good to have the possibility to use line and column
highlighting separately, as well as together.  And it is good to let
users specify the overlay priorities separately.  And it is good to let
users use such highlighting in various ways, including automatically on
idle, to locate the current line/column etc.  Personally, I use only
`crosshairs-mode', binding it to `C-+' to toggle crosshairs on/off quickly.

 
In GNU Emacs 24.0.97.1 (i386-mingw-nt5.1.2600)
 of 2012-05-16 on MARVIN
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.6) --no-opt --enable-checking --cflags
 -ID:/devel/emacs/libs/libXpm-3.5.8/include
 -ID:/devel/emacs/libs/libXpm-3.5.8/src
 -ID:/devel/emacs/libs/libpng-dev_1.4.3-1/include
 -ID:/devel/emacs/libs/zlib-dev_1.2.5-2/include
 -ID:/devel/emacs/libs/giflib-4.1.4-1/include
 -ID:/devel/emacs/libs/jpeg-6b-4/include
 -ID:/devel/emacs/libs/tiff-3.8.2-1/include
 -ID:/devel/emacs/libs/gnutls-3.0.9/include'