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Re: [css3-flexbox] "flex-basis: auto" means completely different things as specified value vs. computed value

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Tue, 5 Jun 2012 19:21:14 -0700
Message-ID: <CAAWBYDBYBZeOiNA9pK-3PBz053BMmyS9OwD5=U1cwTUoGZ97sw@mail.gmail.com>
To: fantasai <fantasai.lists@inkedblade.net>
Cc: www-style@w3.org
On Tue, Jun 5, 2012 at 4:45 PM, fantasai <fantasai.lists@inkedblade.net> wrote:
> The problem we run into here is a terminology one: how is the spec
> supposed to refer to the effective flex basis value? We don't have
> a term for something between the computed value and the used value. :(
> Not that we can't come up with something, but it makes me wonder if
> we're either creating or exposing a systemic problem here.

Yeah, I think we were, so I changed flex-basis so that 'auto' computes
to itself.  The "effective flex basis value" is just the used value of
flex-basis, which is fine, because we don't use it until layout time

> On 06/04/2012 05:25 PM, Daniel Holbert wrote:
>> Assuming we agree on that -- it sounds like you're saying we take the
>> parent's computed value and set it set it as the child's _specified
>> value_. (which might then compute to something else)
>> With that clarification, this is still very bizarre, IMHO.  This means
>> that the "auto" value that I inherit from my parent (in the scenario
>> from my toplevel post) means something *completely* different on my
>> parent vs. what it means on me.  (It means "start flexing at max-content
>> size" on my parent, whereas it means "look at your width property" when
>> I inherit it onto myself.)
> Yes, this is clearly wrong! Maybe the cascade should say that the
> inherited value (the parent's computed value) becomes both the specified
> and computed value on the child?

The assumption when we made the decision was that putting a computed
value into the specified value would make the specified->computed
transition a no-op.  'flex-basis' makes this untrue, since a specified
'auto' turns into a *different* computed 'auto' sometimes.

I think it's best to just watch for violations of this assumption and
change them when necessary.  They should be quite rare, since this is
the first time it's ever happened.

Received on Wednesday, 6 June 2012 02:22:03 UTC

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