[kodablah]

It's about the selector, so the question should be rephrased to "Is there even a use case where CSS needs to select a node based on any field's value?". I think the answer is yes, but it can be limited. But it can become annoying to have a blacklist of attributes that aren't allowed to be selected on.

[sgc]

It's pretty common to check values of a field and set a color to the border etc. based on that, which I think is even very good ui. Maybe browsers should force restricted selectors only on some fields, which only allow limited matching based on predefined character classes or el1 === el2, since it sounds like this could be used for a cross site css attack (perhaps there already were some and I am ignorant).