I would like to discuss about the order of CSS properties in background shorthand.
A bit about the context: Currently getComputedStyle of background shorthand property in webkit does not return the three properties newly added to the background shorthand in CSS3 namely background-size, background-origin and background-clip. We are in the process of adding support for these three properties in getComputedStyle as part of https://bugs.webkit.org/show_bug.cgi?id=86155
If the UAs started generating background shorthand property as per CSS3 spec, that makes it harder for older UAs that supports only CSS2.1 spec (like IE6) to parse these generated results. Also from my testing, I observed that IE6 fails to parse the background shorthand if the order is mentioned as per CSS3 spec. On the other hand if the order of properties in background shorthand gets changed to CSS2.1 order followed by three properties newly introduced in CSS3, older UAs like IE6 can parse all the properties mentioned in CSS2.1 correctly and it ignores the new properties which are added at the end. This will help us to maintain backward compatibility. Latest Opera Browser (v 11.64) generates background shorthand value in getComputedStyle in this order. So the below order will be helpful in maintaining backward compatibility with older UAs