I made a test (attached) for various definition elements to see whether
implementations do in fact look at the conditional processing attributes
on them.
According to the spec, failing conditional processing attributes on
<mask>, <clipPath> and <pattern> should have no effect. There is
nothing mentioned of <filter> or gradient elements, but they seems
similar to the others, so let's assume it should be possible to
reference them too.
In Firefox, rendering of the referencing element is disabled for all of
these elements if they have a failing conditional processing attribute.
This is wrong.
In Opera, you can reference all of these elements and the effect will be
applied. This matches the current spec.
In Chrome, a referenced <clipPath>, <mask> or <pattern> will not be
applied if it has failing conditional processing attributes, but a
<filter> or a gradient element does work.
Given the differences in implementations, I wanted to see whether we are
still happy with the conditional processing attributes having no effect
on <mask>, <clipPath> and <pattern>, and if so whether we should
explicitly handle <filter> and gradient elements in the same way.
