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CSS 3 Comments

From: Brady Duga <duga@google.com>
Date: Thu, 31 Oct 2013 13:31:26 -0700
Message-ID: <CAH_p_eU0L-KBzbO+QKrk6QxG2fXPP6tQPOivj3=+xToFPa6=BA@mail.gmail.com>
To: W3C Digital Publishing IG <public-digipub-ig@w3.org>
OK, here are my comments from a review of CSS 3 Text. If we can get any
others added ASAP, we can try to have these sent out to the CSS WG so they
can have time to review before TPAC.

Comments from Brady

1. It would be great to keep the ‘hanging-punctuation’ property, though I
understand it is awaiting implementations. What is the timeline here? That
is, when would an implementation need to appear in order to preserve this
property?

2. In section 1.3, after the example:
"Within this specification, the ambiguous term character is used as a
friendlier synonym for grapheme cluster. See Characters and Properties for
how to determine the Unicode properties of a character."
"A letter for the purpose of this specification is a character belonging to
one of the Letter or Number general categories in Unicode. [UAX44]"
If I replace 'character' in the second paragraph with 'grapheme cluster', I
am not sure I get a reasonable answer. For instance, is U+0067  + U+0308 a
letter? I don't think U+0308 is, does that disqualify the whole cluster? Or
is this a different use of the term character? Does Unicode define such
clusters as belonging to all the groups all the code points belong to?

3. The only place the spec mentions that text-transform should affect line
breaking is in an informative example (#2), at least that I saw. Should
this be mentioned in a normative section? Some line breaking changes are
obvious (for instance, changing the width of the glyphs will alter line
breaking), but others are more obscure (for instance, transformation to
full width).

4. From 5.1, last bullet point:
"For line breaking in/around ruby, the base text is considered part of the
same inline formatting context as its surrouding content, but the ruby text
is not: i.e. line breaking opportunities between the ruby element and its
surrounding content are determined as if the ruby base were inline and the
ruby text were not there." [Also, note the typo: surrouding]
The first part of this sounds like breaks are allowed in a single run of
base text (difficult, I assume), but the second part sounds like breaks are
only allowed at boundaries of the ruby element. It seems like, in practice,
breaks are allowed anywhere in a ruby element a break would be allowed if
such a location is also a base text boundary.
For example, consider this snippet:
<p>だ<ruby>大分<rt>だいぶ</rt>日数<rt>ひかず</rt></ruby>が</p>
>From "the base text is considered part of the same inline formatting
context as its surrouding content, but the ruby text is not", I might
imagine breaks as though the text were written
だ[1]大[2]分[3]日[4]数[5]が
But, this: "i.e. line breaking opportunities between the ruby element and
its surrounding content" seems to imply this only covers line breaks at the
boundary of the ruby element itself. In which case I would get:
だ[1]大分日数[5]が
However, I would expect the correct breaking would be neither of those, but
rather:
だ[1]大分[3]日数[5]が
I am not certain how I can interpret the spec to generate those line breaks.

5. In "5.2. Breaking Rules for Punctuation", in this sentence and the one
below it that is similar:
"If the content language is Chinese or Japanese, then additionally allow
(but otherwise forbid) for ‘normal’ and ‘loose’:"
It's not clear to me what the 'otherwise' applies to - is it the 'normal'
and 'loose', so it is forbidden in strict when the language is Chinese or
Japanese? Or does it apply to the language as well, so it is forbidden in
strict for Chinese and Japanese, and for any value for all other languages?
If the latter, then the implication is that in eg English, breaks before
 U+2010 are forbidden. However, the later clarifying note seems to indicate
that non-CJK text is only affected when the language is Chinese or Japanese.

6. In "6.1. Hyphenation Control", the sentence: "The UA is therefore only
required to automatically hyphenate text for which [...]"
Is it the case that a UA is ever *required* to automatically hyphenate?
Perhaps this should be weakened to "Therefore, if no language is specified
or no hyphenation resource is available to the UA for a specified language,
the UA may choose to treat 'auto' as 'manual'."

7. Not really wrong, but the order of property names in the title for 6.2
is the opposite of the order just below, in the definition,
‘word-wrap’/‘overflow-wrap’ vs overflow-wrap/word-wrap. Just a little weird.

8. "6.2. Overflow Wrapping", so sayeth Yoda:
"[...] and grapheme clusters must together stay as one unit." Maybe "stay
together" instead?

9. In "7.1. Text Alignment", "text-align: start end" sounds a lot like
"text-align-last: *", giving special treatment to the first line instead of
the last line, with less control. Perhaps there should be a separate
property for controlling the first line alignment, just like there is for
controlling the last line. Then text-align could become a shorthand. For
example:

text-align: center == text-align-first: center, text-align-middle: center,
text-align-last: auto
text-align: center right == text-align-first: center, text-align-middle:
center, text-align-last: right
text-align: left center right == text-align-first: left, text-align-middle:
center, text-align-last: right

This makes the proposed 'text-align: start end' become 'text-align: start
end end' instead.
Of course, the down side is this would require two new properties
("text-align-first", "text-align-middle"). Not sure if this is worth
considering at this point, but it seems odd to handle this in different
ways for different special lines. Perhaps drop 'start end' for now and
reconsider for level 2?

10. What impact do zero-width letters and zero-width word-separators have
on the inter-word and distribute text-justify values?

11. I take exception to example 10 in 7.3.5. Both the greedy algorithm and
the Knuth/Plass algorithm are O(n). What performance metrics are you using
to determine the relative speed of these algorithms? Additionally,
Knuth/Plass is easily adapted to other languages, so it applies equally to
example 11. Perhaps "harder to implement" instead?

12. "8.1. Word Spacing": Can this property be used to make words overlap?
That is, are values less than -100% allowed? 'letter-spacing' says there
may be UA limitations for such things.

13. letter-spacing says it doesn't apply at the start/end of a line. Should
there be similar text be in word-spacing?

14. At the end of word-spacing (just after example 13), the text
"Word-separator characters include [...]" - is this considered an
exhaustive list? If so, this should be made clear, otherwise some sort of
guidelines for deciding what else might be a word-separator would be useful.

15. In "8.2. Tracking", just after example 14: "[...] to the innermost
element element that contains the two characters [...]"
Just one element?

16. And just after example 15: "Letter-spacing ignores zero-width
characters (such as those from the Unicode Cf category)." Does this mean
characters that are defined to be zero-width, or characters whose width
might be zero? For instance, given:

span.zero { display: inline-block; width: 0; }
p {letter-spacing: 1em;}

<p>a<span class="zero">b</span>c</p>

Would this be viewed as "a bc" (1em after 'a', zero-width 'b', 1em after
end of 'b', 'c') or as 'a' with 'b' and 'c' on top of each other 1em later?


17. In "9.1. First Line Indentation", it is not clear to me what
'each-line' is doing. Does this simply make the indent of lines after hard
line breaks indent, and they wouldn't otherwise? If so, perhaps it should
say "In addition to the first line of a block container each line after a
forced line break are also affected. Lines after a soft wrap break are
still not affected." Or maybe there is something else going on I just don't
understand.

18. In "9.2. Hanging Punctuation", the 'Animatable:' table entry has a
spurious gt ('>').

19. Appendix A, steps 5.iv and 5.v - how do you do letter and word spacing
without knowing the font in use? For instance, a percent value for letter
spacing depends on the advance measure of the character, which will depend
on the current font.

19. Appendix B:
"[...]  is to help UA developers to implement default stylesheet [...]" -
'a default stylesheet'? Or maybe 'the default stylesheet'? Or even 'default
stylesheets'?
Received on Thursday, 31 October 2013 20:31:56 UTC

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