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[cssom-view]: offset{Left, Top, Width, Height} for <col> and <colgroup>...

From: Dan Bates <dbates-w3c@intudata.com>
Date: Mon, 14 Mar 2011 15:02:41 -0700
To: <www-style@w3.org>
Message-ID: <f278589454b1ccd05bdd005c0ff9691f@localhost>

I am writing to propose for consideration that offset{Left, Top, Width,
Height} for <col> and <colgroup> return non-zero values. Anne Van Kesteren
suggested that I write to this list after speaking with him on 02/24 on
#whatwg with regards to this issue and my work on WebKit bug #15277
<https://bugs.webkit.org/show_bug.cgi?id=15277>.

In discussing this issue with Anne, we came to the conclusion that table-
columns and column groups do not have have a "CSS layout box" because such
elements only influence aspects of table cells by section 17.3 of the CSS
2.1 spec <http://www.w3.org/TR/CSS21/tables.html#columns>. Hence, these
attributes should return 0 (by section 6.1 of CSSOM View Draft 31
<http://dev.w3.org/csswg/cssom-view/#offset-attributes>).

Instead, I propose that the offset attributes for these table elements
return non-zero values for convenience, consistency with current and
historical browser implementations, and the "box"-like quality they exhibit
via their influence on table cells. I have elaborated on these reasons in
the following list of pros and cons to this proposal:

Pros:
- Consistent with the MSDN documentation for these attributes (see remark
(**)).
- Materially consistent with the functionality of these attributes in IE
and Firefox (see (*))
- Provides a convenient way for a person to access column/column-group
metrics that can be derived by hand from already available metric
information.

Cons:
- Having these attributes return non-zero values disagrees with the
"non-boxness" of <col> and <colgroup> using a strict interpretation of the
CSS2.1 spec.
- Having these attributes return non-zero values disagrees with IE 8
(standards mode), IE 9 (standards mode), and Opera 11.01.
- Will break sites that assume that these attributes will always return 0
for <col>s and <colgroup>s (why?).

(*) Brief Survey of Browser Implementations

Firefox for Mac 3.6.13, IE7, IE8 (quirks mode), IE9 (quirks mode) return
computed values for offset{Width, Height} for <col>s and <colgroup>s.
Firefox for Mac also returns computed values for offset{Left, Top} for such
elements. (IE always returns 0 for these attributes - why?). Opera for Mac
11.01 returns 0 for offset{Left, Top, Width, Height} for <col>s and
<colgroup>s. 

(**) Remark:

>From my understanding the offset attributes were originally introduced as
Microsoft extensions. Notice, the MSDN documentation for these attributes
explicitly state that it applies to <col> and <colgroup>:

offsetLeft:
http://msdn.microsoft.com/en-us/library/ms534200%28v=vs.85%29.aspx

offsetTop:
http://msdn.microsoft.com/en-us/library/ms534303%28v=vs.85%29.aspx

offsetWidth:
http://msdn.microsoft.com/en-us/library/ms534304%28v=vs.85%29.aspx

offsetHeight:
http://msdn.microsoft.com/en-us/library/ms534199%28v=vs.85%29.aspx


For completeness, I have posted a test case that can be used to compare
the value of these offset attributes for <col> and <colgroup> in different
browsers: <http://tersk.intudata.com/~dbates/w3c/col_offset_test.html>.

Dan
Received on Tuesday, 15 March 2011 15:37:56 GMT

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