W3C home > Mailing lists > Public > www-style@w3.org > April 2012

Re: [css3-flexbox] "<flex> can also transition to and from a <length>"

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Fri, 6 Apr 2012 17:29:55 -0700
Message-ID: <CAAWBYDC9XfgGMzUmq-oBzmX3Rt1VZF5svYVmn5QwheQ_iKWsyA@mail.gmail.com>
To: Daniel Holbert <dholbert@mozilla.com>
Cc: www-style list <www-style@w3.org>
On Fri, Apr 6, 2012 at 4:53 PM, Daniel Holbert <dholbert@mozilla.com> wrote:
> Hmm... So on further reflection, I realized that it's problematic for
> transitions to depend on whether or not we're a flexbox item.
> The definition of "flexbox item" depends partly on what the underlying
> element is -- e.g. <img> & <embed> vs <span> & <i>.
> Transitions, however, happen in the style system, so they don't have
> access to what the underlying element is. (at least, they don't in Gecko)
> For example: Suppose we've got "flex:1 0 auto" on both an <img> and a
> <span> inside a flexbox, and then we tweak that to "flex: 10px". The
> spec currently says that the <img> should transition this change,
> whereas the <span> shouldn't -- however, we have no way to figure that
> out from inside the style system.  (Of course, even if we transitioned
> the span, it wouldn't have a visible effect since 'flex' is going to be
> ignored -- still, the intermediate values of 'flex' would be exposed via
> the computed style of the 'flex' property.)
> I think the simplest way to resolve this is just to change "flexbox
> item" to "child of a flexbox" here:
>> The ‘flex’ property is transitionable if the element is a flexbox item
> Thoughts? Does this make sense?

I see what you're saying, but I'm not sure it's as problematic as you assert.

By the time transitions happen, you've already learned what type of
element it is - you needed that information to resolve selectors.  You
might not keep it around for easy reference during transition-time,
though.  That seems fixable, though.  You could just have a "virtual"
property, applied to all the replaced elements, that says whether
they're replaced or not.

I could probably do what you asked for too, though.  I'd just need to
be careful and make sure that "main size property" is defined for
elements that aren't flexbox items.

Received on Saturday, 7 April 2012 00:30:43 UTC

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