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[CSS21] 12.5 Lists: numbering undefined, implementations differ

From: Peter Moulder <peter.moulder@monash.edu>
Date: Wed, 08 Sep 2010 07:28:15 +1000
To: www-style@w3.org
Message-id: <20100907212815.GA8372@bowman.infotech.monash.edu.au>
By "numbering" here, I mean the number as distinct from what string to display
for a given number.

As far as I've seen, there's no text saying what number to give for a given
list-item.  The closest I've seen is an example of an <li> list in an HTML
document; but note that that's an HTML list, whose numbering is [more or less]
defined by the HTML spec, and so doesn't tell us much about how <span
style="display:list-item"> should be numbered, or how list-items in generic XML
documents should be numbered (when styled by CSS).

I append a document with a few tests, to see what existing user agents are doing.
Of the four user agents I tested, no two do the same thing.

In the implementations I looked at, it seems that in an HTML document, <ol> is
special for display:list-item elements even other than <li>; and numbering of
list-items that are descendents of an <ol> element had less variation in
behaviour.

(Looking at WebCore source code, it seems that the test is ol or ul.
A reasonable starting point for the relevant code in WebKit would be
RenderListItem::calcValue.)

<ol> loses its magic in generic XML documents in each of the user agents
whose generic XML behaviour I tested.


Relevant to discussion would be http://www.w3.org/TR/css3-lists (search for
counter; though the main point is that display:list-item implicitly increments
a counter called list-item), and its dependency
http://www.w3.org/TR/css3-content/ for most of the information regarding
numbering.  Whether intentional or not, the numbering appears to be order
within document tree, as modified by pseudo-elements such as :before and :after
(by my reading, though it isn't very clear about this), and as modified by
display:none, but not modified by run-in or 'caption-side' or anonymous block
box processing; and as modified by the suppression of children of
'table-column' boxes and suppression of non-'table-column' children of
'table-column-group', but not modified by the rest of anonymous table object
creation rules.  (Anonymous block processing and anonymous table object
creation don't affect order of boxes/elements, but would be relevant to counter
scope.)

Note that both css3-lists and css3-content are at working-draft status.

Possibly the resolution to this issue would be to note explicitly that CSS2.1
does not define the number assigned to a given list-item, and that this is
expected to be defined by a future level of CSS, probably making some mention
of css3-lists (already in refs.html as #ref-CSS3LIST).


I attach the HTML version of the tests, while the corresponding XML version
(and its associated stylesheets, and the HTML version for good measure) is at
http://bowman.infotech.monash.edu.au/~pmoulder/html-tests/list-item-numbering/

N.B. One of the tests caused a segfault in a WebKit-based browser; if that
happens then comment out the :before rule in the stylesheet.

pjrm.


Received on Tuesday, 7 September 2010 21:28:47 GMT

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