Re: enriched-mode and switching major modes.

[Kim F. Storm]

Some of the existing hook properties may also be used to handle
"delete hard newline betwee paragraphs with different categories" in
some sensible way.

If nothing else, such hooks could set some global value which causes a
post-command-hook to fix whatever conflicts are created by the last
modification -- at least I think that would be more efficient that
relying on jit-lock to run "all the time".

`modification-hooks'
     If a character has the property `modification-hooks', then its
     value should be a list of functions; modifying that character
     calls all of those functions.  Each function receives two
     arguments: the beginning and end of the part of the buffer being
     modified.  Note that if a particular modification hook function
     appears on several characters being modified by a single
     primitive, you can't predict how many times the function will be
     called.

`insert-in-front-hooks'
`insert-behind-hooks'
     The operation of inserting text in a buffer also calls the
     functions listed in the `insert-in-front-hooks' property of the
     following character and in the `insert-behind-hooks' property of
     the preceding character.  These functions receive two arguments,
     the beginning and end of the inserted text.  The functions are
     called _after_ the actual insertion takes place.

     See also *Note Change Hooks::, for other hooks that are called
     when you change text in a buffer.

`point-entered'
`point-left'
     The special properties `point-entered' and `point-left' record
     hook functions that report motion of point.  Each time point
     moves, Emacs compares these two property values:

        * the `point-left' property of the character after the old
          location, and

        * the `point-entered' property of the character after the new
          location.

     If these two values differ, each of them is called (if not `nil')
     with two arguments: the old value of point, and the new one.

     The same comparison is made for the characters before the old and
     new locations.  The result may be to execute two `point-left'
     functions (which may be the same function) and/or two
     `point-entered' functions (which may be the same function).  In
     any case, all the `point-left' functions are called first,
     followed by all the `point-entered' functions.

     It is possible with `char-after' to examine characters at various
     buffer positions without moving point to those positions.  Only an
     actual change in the value of point runs these hook functions.

-- 
Kim F. Storm <address@hidden> http://www.cua.dk