Some wiki pages have multiple authors. It seems logical that you would use multiple meta directives to mark this,

[[!meta  author="author one"]]
[[!meta  author="other author"]]

however, when you do this, it appears that things that key off of the author tag only pick up on the last instance of the directive. for example a page spec looking for

author(author one)

will not match while one looking for

author(other author)

will match. I would expect that both would match.