Re: [cgmo-webcgm] SV, CV and CSS2-like inheritance [was: Re[2]: [cgmo-webcgm] Style properties]

[Benoit Bezaire <benoit@itedo.com>]

Hi Lofton,

See inline...

Tuesday, May 17, 2005, 8:14:39 PM, Lofton wrote:

LH> At 02:58 PM 5/17/2005 -0400, Benoit Bezaire wrote:
>>[...]
>>LH> A.) If the Computed Value of a style property involves "convert to
>>LH> absolute",
>>LH> B.) and if we inherit the Computed Value,
>>LH> then .... it creates problems for CSS2-like inheritance of style
>>LH> properties.
>>What are these A) and B)? I'm not sure I'm following your line of
>>thoughts here?

LH> Okay, A and B are two factors or conditions that, taken together, make it
LH> difficult to apply the CSS2 model, unmodified, to our style properties
LH> inheritance.  We are talking about inheritance down a tree of APSs.

LH> A.) CSS2 says that convert-to-absolute happens at the Computed Value stage.

LH> [Stroke-weight is a property of an APS.  If convert-to-absolute for
LH> stroke-weight means that you must convert % to NVDC, this cannot be done at
LH> the APS level.
Why can't this be done at the APS level?

LH>   So the CV of stroke-weight is ill-defined at the APS level,
LH> if the CV requires convert-to-absolute.]

LH> B.) CSS2 says that Computed Values are inherited.  (CSS3 allows each
LH> property to define which type of value is inherited.)

LH> Condition A and condition B taken together makes it problematic to apply
LH> the CSS2 inheritance model exactly to our style properties inheritance.
Why is it problematic?

-- 
 Benoit   mailto:benoit@itedo.com

 
LH> If we relax condition B, i.e., if we say that SV is inherited down APS
LH> branches (for style properties) instead of CV, as allowed by CSS3, then
LH> that inheritance model works.  (But it leaves CV pretty much unused in the
LH> model, and doesn't solve the problem of uncomputable CV at the APS level.)

LH> If we relax condition A -- i.e., convert-to-absolute happens after CV,
LH> e.g., at the Used Value stage -- then CV is the same as SV (except for
LH> resolution of the values 'inherit', which we don't allow anyway for style
LH> properties.)  And inheritance down APS branches works, CSS2-like.

LH> -Lofton.