Basically I know how "a" and "an" are used:
a member
an adult member
but how is the same handled when the middle word is inserted parenthetically or even in brackets:
I met a member of the club.
I met a/an - adult - member of the club.
I met a/an (adult) member of the club.
Should there be "a" used, because the main phrase is "a member" or should "an" be used because the adjective starts with a vowel? And is there a rule to quote?