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[css3-text] puzzling new definition of expansion opportunity

From: John Daggett <jdaggett@mozilla.com>
Date: Wed, 5 Jun 2013 05:37:51 -0700 (PDT)
To: W3C Style <www-style@w3.org>
Message-ID: <57870562.20308786.1370435871933.JavaMail.root@mozilla.com>

Since the last published WD last November, a new definition of
expansion opportunity has been added to the CSS3 Text spec:

# CSS defines expansion opportunities as points where the
# justification algorithm may alter spacing within the text. Expansion
# opportunities are divided into different priority levels: within a
# level, all expansion opportunities are expanded or compressed at the
# same priority, with space distributed in proportion to the expansion
# opportunity’s ‘font-size’. In the case of an expansion opportunity
# introduced by a single character, (as with ‘word-spacing’) the
# ‘font-size’ of that character is used; in the case of an expansion
# opportunity between characters, (as with ‘letter-spacing’) the
# ‘font-size’ of the innermost element containing their boundary is
# used. 

What is this trying to control?  Lines where the font size varies
across the line, such that expansion would be smaller around smaller
characters?  Is this what user agents do now with word-spacing?  Why
is it necessary to include this level of complexity?

At the very least I don't think this is adequately specified to a degree
such that two implementations would have the same behavior.

Regards,

John Daggett
Received on Wednesday, 5 June 2013 12:38:22 UTC

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