There's no "attached" identifier in the specification of the shaders. In order to be verbose when calculating the computed style we need an "attached" identifier. Verbose mode means that even if the default mode is "attached", we will have an "attached" identifier in the output of the computed style. Adding this bug to make sure an "attached" mode is added to the spec, OR remove the comment in the code saying that the computed style will not contain any "attached" identifier. example: -webkit-filter: custom(url(vertex), 10) should compute to -webkit-filter: custom(url(vertex) none, 10 10 attached) Currently, we cannot compute to the string with "attached", because accordingly to the spec it is not a valid syntax.
I am a bit confused. Do you mix up computed values and computed style in the description? The computed value should have attached. The computed style shouldn't, if you didn't specify it. Even it the computed value has it :P
Spoke with achicu on IRC. This part of CSSComputedStyleDeclaration is deprecated now and will be removed soon after finishing the new syntax for custom(). Closing this bug as invalid.