[feature request] support for getting short form version

[hrj]

I am not sure if this needs to be in jStyleParser; but it seems relevant. Would like to know your thoughts on this. Thanks!

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The CSS DOM API allows querying the short hand form of a property, even when it is not directly specified. There are two types of behaviour:

1. In JS, element.style.background returns the background as specified in the style attribute.
2. In JS, getComputedStyle(element).background returns the short form of the computed background, even if only long forms are specified.

It would be nice to have some support for this from jStyleParser (in the form of static utility methods). The wiring to JS land can be done on the client side of course.