Today I tried to ask a question with tag regex and got rejected with:
Oops! Your question couldn't be submitted because: Creating the new tag [regular-expressions] is not allowed since the tag [regular-expression] already exists. If you think this new tag should be allowed, raise it on meta.
I didn't type "regular-expressions" so I assumed that "regex" was aliased to it, before it became outdated/superceded by "regular-expression".