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Re: (X)Emacs abbrev mode
From: |
Stefan Monnier |
Subject: |
Re: (X)Emacs abbrev mode |
Date: |
Wed, 24 Feb 2010 16:48:31 -0500 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.1.92 (gnu/linux) |
>>> I was wondering if you could tell me why the following works in XEmacs and
>>> not in Emacs.
>> Because Emacs only accepts "words" as abbreviations by default.
>> If you want to support something else (i.e. abbreviations that contains
>> chars that are not marked as words in the syntax-table), then you need
>> to tweak your abbreviation table by setting its :regexp property.
> as this question comes into my mind from time to time: is there any reason
> to limit the chars usable as abbrevs at all?
Obviously, no good one since XEmacs does it.
As for the not-so-good ones:
- limiting them to word-chars means that you can just "grab the word
before point" and then "look it up in the table". Whereas XEmacs
can't do that and has to loop through the table and check each and
every abbrev to see if the text before point happens to be one
of them.
- there is implicitly a notion of "boundary" that's important. E.g. if
"foo" is an abbrev, you don't want it to apply to "afoo". OTOH you do
want it to apply to ",foo". The abbrev definition never makes this
boundary specification clear. IIUC XEmacs uses a heuristic which is
that if the abbrev starts with a word-component then it only matches
if the char before is not itself a word-component (i.e. this
reproduces the convention used in Emacs) and that if the first char of
the abbrev is not a word-component than it is its own boundary so an
abbrev "\foo" will also be expanded when the text before point is
"\\foo" for example.
-- Stefan