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bug#20613: Font locking is poorly documented
From: |
Paul Eggert |
Subject: |
bug#20613: Font locking is poorly documented |
Date: |
Tue, 19 May 2015 15:42:05 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 |
I was recently urged to use font locking to support a feature in Emacs,
and I must say that I am still confused about how it works even after
reading the Elisp manual several times. The manual has a lot of
low-level discussion of mechanism, but it doesn't explain policy and
since crucial features seem to be undocumented, I'm at a loss as to how
to use it, or how to debug it when it's not working. I finally gave up
and used Google and found cookbook stuff, but I have no idea how or why
it works as well as it does, or why it fails when it does. For example:
http://www.emacswiki.org/emacs/PrettyLambda
gives this example:
(defun pretty-lambdas ()
(font-lock-add-keywords
nil `(("(\\(lambda\\>\\)"
(0 (progn (compose-region (match-beginning 1) (match-end 1)
,(make-char 'greek-iso8859-7 107))
nil))))))
but I can't find documentation explaining why a progn is needed, or why
it must return niil, or why one must use compose-region, or why one must
use it with a single λ rather than just having a λ character there.
One small suggestion: add a section explaining how the above example works.
- bug#20613: Font locking is poorly documented,
Paul Eggert <=