I agree. From your (both of you) comments, it could be understood that the fact that some element takes up space when hidden may be a side effect, a bug, or a particularity of some renderer. I just wanted to point out that that is exactly what "visibility:hidden" is supposed to do and the reason why one may want to use it in some specific cases, it's not a side effect.
And yes, "display:hidden" is wrong, or a mistake, as I said, for "display:none" or "visibility:hidden". Which is the right one, depends on what one wants. (And in ePub 2, "visibility" is not a required property.)
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