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[css3-lists] position:marker and compatibility with existing 'outside' implementations/content

From: Øyvind Stenhaug <oyvinds@opera.com>
Date: Fri, 17 Aug 2012 17:52:13 +0200
To: "www-style@w3.org" <www-style@w3.org>
Message-ID: <op.wi6zpbc3bunlto@oyvinds-desktop>
Since I heard feedback on marker positioning was requested, I wrote down  
some comments. I really only looked at the positioning of 'outside'  
markers with respect to what can already be specified with CSS 2.1 syntax.

It's possible I have misunderstood some parts of the spec, e.g. with  
regards to the placeholder thing. If my assumptions are wrong, I think the  
text needs to be clarified.

In general, the model seems quite simple, which is often a good thing.  
However, in some cases it seems all major implementations would need to  
change, which makes me wonder if there would be compat issues.

1) Unless the rumored part about placeholders in css3-positioning (an  
inline text search turned up nothing) is something quite different than  
what happens with regular absolute positioning, the spec doesn't consider  
that an 'outside' list marker may cause an empty, non-zero-height linebox  
to be created (or at least cause the auto height of an empty list-item to  
become non-zero). For instance, all browsers I tried  
(Chrome/Firefox/IE9/Opera) show two list markers and green background here:

<!doctype html>
<style> li { background: green; }</style>
<ol>
<li></li>
<li></li>
</ol>

2) Similarly, a big 'outside' list-style-image marker can affect the  
height of an existing linebox. E.g. add list-style-image: url(/* URL to a  
100px*100px image*/) to the above case (and optionally some text in the  
LIs) - no browser allows the images to overlap.

3) Given the above, it seems basing the block axis position on the  
'inside' position (= immediately before the list-item's '::before') will  
cause empty lines to appear more often than they do in Firefox/Opera.  
Though maybe this was intentional, since "spec is similar to what IE does,  
because that was sanest" as the IRC log for 2012-08-15 states.

4) However, even so, the vertical alignment will be off if, for instance,  
the list-item's contents start with a block that has vertical padding  
and/or borders. Not even IE uses the hypothetical 'inside' position in  
this case.

5) No special attention is given to floats. For instance, here the marker  
will overlap the float (and will be a long distance away from the text  
that starts the line):

<!doctype html>
<style>
    div {
       float: left;
       width: 100px;
       height: 100px;
       background: gray;
       margin-right: 40px;
    }
</style>
<div></div>
<ul><li>list-item</li></ul>

That doesn't happen in Firefox or Gecko, though it does in IE9 and Opera  
with Presto>=2.9 or thereabouts. Since changing, we've seen some issues  
popping up in the wild about this (e.g. on Wikipedia).

-- 
Øyvind Stenhaug
Core Norway, Opera Software ASA
Received on Friday, 17 August 2012 15:52:44 GMT

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