CSS Variables is a feature that allows authors to define custom
properties that cascade and inherit in the same way that regular
properties do, and to reference the values of these custom properties in
the values of regular properties (and other custom properties too).
http://dev.w3.org/csswg/css-variables/
I blogged about the feature when it initially landed here:
http://mcc.id.au/blog/2013/12/variables
It lives behind the layout.css.variables.enabled pref, which is
currently enabled by default only on Aurora/Nightly.
One thing from the specification that we don't implement is the
CSSVariableMap, but Tab tells me that this is going to be removed from
the spec.
I intend to enable this feature by default this Friday (March 21). That
would target Firefox 31.
The spec has been stable for a while, and the CSS Working Group already
has a resolution to publish the document as a Candidate Recommendation.
There has been a last minute proposal for a change to the syntax of
custom property declarations, to align with other custom features in CSS
that are coming down the pipeline (such as custom media queries). There
are a couple of proposals on the table: to replace the "var-" prefix of
the name of the custom property with a "_" prefix, or perhaps just
anywhere within the name. Similarly for "--" rather than "_".
Tab wants to discuss this in this week's CSS Working Group telcon, so if
the decision is made quickly enough we can update our implementation.
The CSS Working Group is aware of our plans to ship.
Bug to enable this feature:
https://bugzilla.mozilla.org/show_bug.cgi?id=957833
Blink until recently had an implementation of CSS Variables, behind a
flag, but not one that supported the fallback syntax (or
CSSVariableMap). They have recently removed it saying that they need to
rewrite as it had poor performance, but they say they are still
interested in the feature.
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