GNU bug report logs - #4114
23.1; face doc unclear - no explanation of "underlying" face or attribute value

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Message #11 received at 4114-done <at> emacsbugs.donarmstrong.com (full text, mbox):

From: "Drew Adams" <drew.adams <at> oracle.com>
To: "'Chong Yidong'" <cyd <at> stupidchicken.com>
Cc: <4114-done <at> debbugs.gnu.org>
Subject: RE: 23.1; face doc unclear - no explanation of "underlying" face or attribute value
Date: Sat, 15 Aug 2009 14:53:20 -0700

> > In (elisp)Face Attributes, things are explained in terms of
> > "underlying" face. But this notion is never introduced or explained.
> 
> Thanks, I've tweaked the text and added a reference to the node
> Displaying Faces, where the concept is explained.

Thanks; that's clearer.

However:

1. "Underlying face" is defined as "a face that has a lower priority in the
list...". That begs the question, "lower than what"? Lower than some other face,
presumably (?), but which one? (This passage is about fonts.) I think we need to
specifically speak of a given face underlying another given face (or perhaps
underlying a faceless set of face attributes?).

2. Related to #1. It's not clear to me whether there is only one underlying face
for a given face/font/attribute-set (?). You say "a face", not "the face", so I
guess there can be more than one that has a lower priority. But then you speak
of "the underlying face".

Probably this text just needs a little more tweaking, but for the moment it is
still not clear to me.

Also, I think the same kind of clarification (e.g. with an xref) is needed in
node Attribute Functions (see `merge-face-attribute'), where it also refers to
"underlying".

> > I have no idea what was intended in any of these passages.
> 
> Here's an experiment that should make this clear.  Go to the default
> *scratch* buffer and evaluate the following lines, one at a time:
> 
> ;; Give the comments in this buffer a height of 15.
> (set-face-attribute 'font-lock-comment-face nil :height 150)
> ;; Give characters 5 to 8 a height that's 0.9 times that of the
> ;; underlying face, in this case font-lock-comment-face.
> (setq ov (make-overlay 5 8))
> (overlay-put ov 'face (list :height 0.9))

OK, that example seems clear; thanks. In this case, the face that's higher
priority is the one set by `overlay-put'. The face that has lower priority is
`font-lock-comment-face'.

The questions mentioned above are still not clear to me, however. Thx.

--

I see that you just now closed this bug. You close bugs too quickly. I don't
know if now this reply will even get added to the bug thread, without my having
to reopen the bug. IIRC, once a bug is closed, no further feedback is possible.

I don't reaslly need the bug reopened in this case, if you will please at least
take this feedback into account - I think a little more clarification would
help.

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