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[css-display] Unofficial draft of a Display spec ready for consumption

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Fri, 19 Oct 2012 15:40:32 -0700
Message-ID: <CAAWBYDB-MnkJm5q4acmama_1xDeU_qEYJpUKEf3V_6b23iD4KA@mail.gmail.com>
To: www-style list <www-style@w3.org>
Hey all!  I've been complaining for some time about the fact that
'display' unnecessarily conflates "layout mode" with "role in parent's
layout mode".  I've had mini-rants about this in Lists and Flexbox,
and on the list a lot of times.  Further, authors have given
consistent feedback over the years that indicates the conflation of
'display:none' with the other values is confusing or hard to work with
- in particular, they'd like to be able to toggle "none"-ness without
disturbing the original 'display' value, or having to manually
remember what the old value was.

As such, I've written up a first draft of a proposal to split
'display' into sub-properties:
<http://dev.w3.org/csswg/css-display-3/>.  (It currently has the ED
styling, but as I've indicated in the Status section, it's technically
an Unofficial Draft until the WG approves it.)

There's some prior art for this draft.  Old revisions of the Template
Layout draft included 'display-model' and 'display-role' properties,
which were cognates to 'display-inside' and 'display-outside' in my
draft.  Over two years ago I authored a blog post
<http://www.xanthir.com/blog/b45F0> exploring the idea.

This draft actually introduces very little new functionality.  The
most important innovation is just that several independent concepts
that were previously wrapped together in 'display' are now separated,
so they can be independently toggled/cascaded.  In particular, an
element's layout mode is determined by 'display-inside', while the
element's role in its ancestor's display mode is determined by
'display-outside'.  The "display:none" functionality is handled by the
'display-box' property, while the generation of ::marker
pseudo-elements is controlled by 'display-extras'.  (Both of these
latter property names are pretty sucky.  Feel free to bikeshed them.)

The only fundamentally new pieces of functionality are:

1. Any type of element can generate a ::marker pseudo. ::marker is
exactly like ::before, except that it has some special positioning and
content rules in Lists, so this is nothing particularly special.  It
just falls out of the model more-or-less by accident.
2. You can toggle between "display-box: normal;" and "display-box:
none;" without affecting the element's layout mode or role.
3. 'display-box' has a new value, "contents", which has been requested
and talked about in the past - it suppresses the element's own box
generation, but not that of its children - in other words, for layout
purposes it acts as if the element was replaced by its children.  This
is useful for layout modes, like Flexbox, that privilege children over
arbitrary descendants, because sometimes you need a wrapper element
(for script or cascade purposes), but still want the children of the
wrapper to interact with the non-wrapper elements around them.  It's
also useful for Web Components, for similar reasons - many things are
vastly simplified by making the shadow root a wrapper element, but the
extra element can make layout harder.

Thoughts?  Would the WG be okay with taking this on as a work item?
It should be low-maintenance and pretty quick to advance, because I'm
not trying to do very much with it.  In particular, I'm *not* wanting
to mix any block-layout-related stuff into this draft - that should be
done in an explicit Block Layout spec (Anton, your calling!).  That
said, there's the potential for a little more work going on in this
spec.  I have issues called out inline for additional things we could
usefully put into the draft.

~TJ
Received on Friday, 19 October 2012 22:41:20 GMT

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