[css-typed-om] spec should clarify inheritance of CSSImageValue from CSSResourceValue for non-network image types

[dbaron]

Right now the spec has a sequence of interfaces that inherit from the following one: CSSURLImageValue : CSSImageValue : CSSResourceValue. No other interfaces currently inherit from any of these types.

However, it seems like in the future there will be value types for other CSS image types, such as gradients. It seems logical that a CSSGradientValue type would inherit from CSSImageValue.

However, this raises the question of how CSSResourceValue should behave when it doesn't represent something that needs to be loaded from the network. It seems to me that either:

• the current CSSResourceValue spec should specify that, or
• another inheritance hierarchy should be used so that gradients wouldn't end up inheriting from CSSResourceValue

[dbaron]

Oh, I guess this is specified in the CSSImageValue section:

CSSImageValue objects that do not require network data (for example linear and radial gradients) are initialized with state "loaded".

But it seems like this should instead be in the spec for CSSResourceValue.