W3C home > Mailing lists > Public > public-texttracks@w3.org > May 2012

[Bug 17218] New: Wrong approach for line breaking rules

From: <bugzilla@jessica.w3.org>
Date: Mon, 28 May 2012 10:44:19 +0000
To: public-texttracks@w3.org
Message-ID: <bug-17218-5018@http.www.w3.org/Bugs/Public/>

           Summary: Wrong approach for line breaking rules
           Product: TextTracks CG
           Version: unspecified
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: WebVTT
        AssignedTo: ian@hixie.ch
        ReportedBy: simonp@opera.com
         QAContact: dave.null@w3.org
                CC: mike@w3.org, public-texttracks@w3.org

Text runs must be wrapped according to the CSS line-wrapping rules, with the
following additional constraints: 
* Regardless of the value of the 'white-space' property, lines must be wrapped
at the edge of their containing blocks, even if doing so requires splitting a
word where there is no line breaking opportunity. (Thus, normally text wraps as
needed, but if there is a particularly long word, it does not overflow as it
normally would in CSS, it is instead forcibly wrapped at the box's edge.)
* Regardless of the value of the 'white-space' property, any line breaks
inserted by the user agent for the purposes of line wrapping must be placed so
as to minimise Δ across each run of consecutive lines between preserved
newlines in the source. Δ for a set of lines is defined as the sum over each
line of the absolute of the difference between the line's length and the mean
line length of the set.

We are not happy with this requirement. There are several problems.

The first bullet point is already available in CSS with word-wrap:break-word.
We don't want to have two *slightly* different ways to force word wrapping just
because the requirement here is differently worded than the CSS feature. Just
say that word-wrap:break-word be applied by default (and this property could be

We don't want to wrap when white-space is pre or nowrap. We basically don't
want to derivate from CSS behavior.

The balanced line wrapping rules is overly precise. Since it is largely
undefined in CSS where line break opportunities are, it seems inappropriate to
have precise rules for balancing, and UAs should be allowed to approximate the
balancing for perf.

So, what we want is:

* Remove the quoted spec text.
* Add word-wrap:break-word; as a default style.
* Relax the balancing algorithm.

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Received on Monday, 28 May 2012 10:44:27 UTC

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