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Re: W3C 'CSS3 module: Color' Working Draft dated 19th February 2002

From: Tantek Çelik <tantek@cs.stanford.edu>
Date: Wed, 20 Mar 2002 11:37:00 -0800
To: Daniel Steinberger <Daniel.Steinberger@gmx.de>, "Tantek Çelik (Microsoft Corporation)" <tantekc@microsoft.com>, "Chris Lilley (W3C)" <chris@w3.org>, "Steven Pemberton (CWI)" <steven.pemberton@cwi.nl>, "Brad Pettit (Microsoft Corporation)" <bradp@microsoft.com>, www-style@w3.org
Message-id: <B8BE24DB.4017%tantek@cs.stanford.edu>
The ability to control opacity on particular pieces of an element is
provided by the new rgba() or hsla() color values as defined in the CSS3
Color Module.

For background image transparency, use PNG.

The working group considered, but decided against, introducing new
properties such as you propose, because we would have had to have introduced
several new properties:
 background-opacity
 foreground-opacity
 text-decoration-opacity
 border-opacity (perhaps also border-top-opacity, border-right-opacity,
border-bottom-opacity, border-left-opacity)
 outline-opacity

This would have been necessary because although you assert that
foreground-opacity would apply to the border, it was also shown that one
might want the border to be as transparent as the background.  As such, we
couldn't assume that foreground-opacity would have (or have not) applied to
text-decoration and outline etc.
 
It is much simpler to introduce 2 new color value types which can then be
used with all properties that specify a color, rather than add 5-9 new
properties.

In addition, the new color value types permit controlling the opacity of
these pieces of elements independently of elements' children, which the
opacity property does affect.

As far as inheriting the property, for consistency, all properties in CSS2
(and CSS3 for that matter) accept the 'inherit' value.

Regarding accepting percentages for opacity - given how percentage values
work for other types (typically depending on the parent), it was decided
that it would have been confusing to allow percentage on opacity, since that
percentage would not be a percentage of some property of the parent.  So,
for simplicity and clarity, it was decided to just use <alphavalue>.

Thanks for your feedback,

Tantek




On 3/20/02 8:40 AM, "Daniel Steinberger" <Daniel.Steinberger@gmx.de> wrote:

> Dear editors,
> 
> I'd like to make a proposal to the 'opacity'
> [http://www.w3.org/TR/css3-color/#opacity]
> property of the 'CSS3 module: Color' module.
>
> ...
> 
> So now my proposal:
> 
> I suggest introducing
> properties for each nessesary type of elements:
> 
> Name:        opacity-background
>
> ...
>
> Name:        opacity-foreground
> 
> ...
>
> Note 1: As described in the paragraph about inheriting
> the property, I don't see the use of being able to
> inherit the value.
>
> ...
> 
> Note 2: I think it might be OK to permit percentages as
> well, since they can be easily translated to <alphavalues>
> (e.g. '20%' corresponds to '0.2').
>
> ...
> 
> Please consider my feedback and let me know your opinion
> about this proposal. Thank you very much.
> 
> --Daniel Steinberger
> 
Received on Wednesday, 20 March 2002 14:34:23 GMT

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