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Re: opacity in css

From: Peter S. Linss <peter@linss.com>
Date: Tue, 27 Mar 2001 15:04:15 -0800
Message-ID: <3AC11C6E.5DAAB365@linss.com>
To: James Craig <james_craig@Powered.com>
CC: www-style@w3.org
FYI: the "-name-" prefix is the officially sanctioned mechanism for adding
experimental or proprietary keywords to CSS. It was done that way because: 1) no
normally valid keyword may begin with a '-' character; and 2) to "namespace"
nonstandard keywords to prevent collisions with extensions from other vendors
that may not behave in the same manner (if they all behaved the same way it
would be "standard behavior" and would be in the spec).

Many mozilla extensions, like opacity and border-radius have been proposed to
become part of the standard and are considered experimental implementations. The
"-moz-" prefix will be dropped (but still supported for backward compatibility)
when/if it becomes part of the standard. Another benefit of having the prefixed
version is that the CSS committee is free to modify the syntax or behavior of
the property when adding it to the spec and legacy stylesheets will still work
against the prefixed version. The committee does not then feel compelled to
adhere to the experimental version to avoid breaking compatibility with existing
style sheets if a better way of doing it presents itself.

So '-moz-opacity' isn't really a branching, but an attempt to create a
standarized property without stepping on anyone's toes.

IEs 'filter' predated Mozilla's opacity as well as the prefixing mechanism for
extensions. It has been proposed for inclusion in the standard (and rejected in
its current form) several times.

James Craig wrote:

> this might have been discussed before i got on the list, sorry.
>
> it's great that with ie6 coming out that browsers should be up to par with
> xhtml, css, and dom specs, but i just noticed that netscape and ie seem to
> be branching off again when it comes to certain things.
>
> some of the ie 'filters' that were left out of the css spec seem pretty
> useful (specifically 'opacity')... today i found out that ns6 supports
> opacity but in a different way.
>
> IE:
>  filter:alpha(opacity=50);
>
> NS6:
>  -moz-opacity:0.5;
>
> of course, neither works in Opera.
>
> now at first i thought it was stupid to stick the mozilla name in a css tag,
> but the more i thought about it, the more i liked the idea of them stating,
> "we know it's not in the spec, but here's how we (-moz-/mozilla) would have
> done it."
>
> it also seems better supported in ns. in ie, to apply a transparency to an
> object (other than an image) the object has to be absolutely positioned.
>
> regardless of the details, my discussion topic for the group is: what do you
> think about this functionality branching again? ns4 vs ie4 caused me many
> headaches and i see it going the same way again... it would be nice to avoid
> the headaches, any thoughts?
>
> james craig
>
> ps. when i intalled the IE6 public preview, it deleted my copy of IE 5.5...
> is this and official release, is this a bug, or did it hide 5.5 somewhere?
> thanks.
> http://msdn.microsoft.com/workshop/author/css/overview/CSSEnhancements.asp
Received on Tuesday, 27 March 2001 18:04:46 GMT

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