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(elisp)Overlay Arrow

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The Overlay Arrow
=================

   The "overlay arrow" is useful for directing the user's attention to
a particular line in a buffer.  For example, in the modes used for
interface to debuggers, the overlay arrow indicates the line of code
about to be executed.

 - Variable: overlay-arrow-string
     This variable holds the string to display to call attention to a
     particular line, or `nil' if the arrow feature is not in use.  On
     a graphical display the contents of the string are ignored;
     instead a glyph is displayed in the fringe area to the left of the
     display area.

 - Variable: overlay-arrow-position
     This variable holds a marker that indicates where to display the
     overlay arrow.  It should point at the beginning of a line.  On a
     non-graphical display the arrow text appears at the beginning of
     that line, overlaying any text that would otherwise appear.  Since
     the arrow is usually short, and the line usually begins with
     indentation, normally nothing significant is overwritten.

     The overlay string is displayed only in the buffer that this marker
     points into.  Thus, only one buffer can have an overlay arrow at
     any given time.

   You can do a similar job by creating an overlay with a
`before-string' property.  Note: Overlay Properties.