@supports test

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CSS3 spec

This page studies the @supports rule in a few specific situations.

So far mostly tested on desktop. Mobile tests will follow later (I hope).

background-attachment

The problem with this declaration is that most mobile browsers support either local or fixed, but not both. Some don’t even support one of the two. As I read the spec, they should report that they do not support the values that don’t actually do anything useful. But they declare support for both, which is wrong.

transition-property

With the exception of Safari, all browsers will always claim support for any value of transition-property; even nonsense. This is obviously wrong.

More subtle is the case of display. Yes, it’s a valid property name, and thus a valid value for transition-property, but you can’t actually transition a display declaration. Should @supports still claim support, even if it does nothing useful?

Support

So far @supports only works on declarations and values; not on selectors or media queries. Pity, but such is life.

The syntax of the examples may actually appear a future version of the spec. On the other hand, it may not.

Other

Other stuff I tested that is all correct.