The auto-overlays package automatically creates, updates and destroys overlays based on regular expression matches in the buffer text. The overlay is created when text is typed that matches an auto-overlay regexp, and is destroyed if and when the matching text is changed so that it no longer matches.
The regexps are grouped into sets, and any number of different sets of regexps can be active in the same buffer simultaneously. Regexps in different sets are completely independent, and each set can be activated and deactivated independently (see Defining Regexps). This allows different Emacs modes to simultaneously make use of auto-overlays in the same buffer.
There are different “classes” of auto-overlay, used to define
different kinds of overlay behaviour. Some classes only require a single
regexp, others require separate regexps to define the start and end of
the overlay (see Defining Regexps). Any additional regexps, beyond
the minimum requirements, act as alternatives; if more than one of the
regexps matches overlapping regions of text, the one that appears
earlier in the list will take precedence. The predefined regexp classes
flat, but the auto-overlay package can easily be extended with
Note that for efficiency reasons,
self overlays are not
fully updated when a new match is found. Instead, when a modification is
subsequently made at any position in the buffer after the new match, the
overlays are updated up to that position. The update occurs just
before the modification is made. Therefore, the overlays at a
given buffer position will not necessarily be correct until a
modification is made at or after that position (see To-Do).
By default, the entire text matching a regexp acts as the
“delimeter”. For example, a
word overlay will cover all the
text matching its regexp, and a
nested overlay will start at the
end of the text matching its start regexp. Sometimes it is useful to be
able to have only part of the regexp match act as the delimeter. This
can be done by grouping that part of the regexp (see Defining Regexps). Overlays will then start and end at the text matching the
group, instead of the text matching the entire regexp.
Of course, automatically creating overlays isn't much use without some way of setting their properties too. Overlay properties can be defined along with the regexp, and are applied to any overlays created by a match to that regexp. Certain properties have implications for auto-overlay behaviour.
priorityproperties, regexp matches within the overlay are ignored if they have lower priority. An example use is ignoring other regexp matches within comments in code.