Should data.specifications explicitly exclude the CSSInfo macro?

[ddbeck]

While fixing CSS pages' errors, I've noticed a pattern: when I add data.formal_definition (which includes a {{CSSInfo}} call), I check the page for that macro call elsewhere. It's usually in the data.specifications section and I delete it.

That is, if I remember to look and make the change. It occurred to me that we could regularize this check by either explicitly forbidding macros other than SpecName from data.specifications or, more narrowly, forbidding the CSSInfo macro from the ingredient.

This would be a pretty easy change to make to the spec and ingredient handler. Should we do it? What considerations might I be missing? I'd appreciate your input on this @Elchi3, @wbamberg, and @chrisdavidmills.