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[csswg-drafts] [css-text-3] Assorted editorial clarifications/requests (#3461)

From: Myles C. Maxfield via GitHub <sysbot+gh@w3.org>
Date: Wed, 19 Dec 2018 18:53:13 +0000
To: public-css-archive@w3.org
Message-ID: <issues.opened-392733650-1545245592-sysbot+gh@w3.org>
litherum has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-text-3] Assorted editorial clarifications/requests ==
> Form feeds (U+000C) (that are not segment breaks) are rendered as a zero-width space (U+200B).
> ...
> If the character ... is the zero-width space character (U+200B), then the break is removed

Unclear whether or not the form feed causes breaks to be removed.

Also, "rendered as a zero-width space" is probably not what you want. Zero-width spaces can participate in text shaping inside the font, and some fonts even have visible glyphs for zero-width-space that get removed by shaping. Why doesn't the spec say they're removed instead of rendered as U+200B?

> If the character immediately before or immediately after the segment break is the zero-width space character (U+200B), then the break is removed, leaving behind the zero-width space

Similarly to above, leaving behind the ZWS is probably not what you want, as it can participate in shaping. It seems CSS is trying to treat the ZWS as a flag to signal behavior for the following break; leaving the flag behind seems like pollution.

Vaguely related: One of the things I'd like to do in WebKit is to forcibly not render ZWS under all circumstances using all fonts. After shaping, we would trace back each glyph to determine which character it came from, and if it came from a ZWS, literally delete the glyph from the sequence of glyphs.

> As required by [UNICODE], unsupported Default_ignorable characters must be ignored for rendering.

A more useful link would be appreciated, instead of linking to the Unicode homepage.

> As with spaces, any collapsible segment break immediately following another collapsible segment break is removed.
> ...
> Any space immediately following another collapsible space ... is collapsed to have zero advance width.

These sentences seem contradictory. "Removed" is not "collapsed."

> break is F, W, or H (not A)

Please spell these terms out. I had to go digging through specs to figure out which classes these letters correspond to.

* It took me a while to figure out what the Segment Break Transformation Rules were trying to accomplish. An example showing uninterrupted Chinese text would be appreciated.

> In some other writing systems, soft wrap opportunities...

This paragraph seems non-normative. Perhaps move it to a note?

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/3461 using your GitHub account
Received on Wednesday, 19 December 2018 18:53:14 UTC

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