02br 02br 01i 00Quirk et al02i 00 call that is an 'appositional conjunct', and a nonrestrictive one at that. In another section they indicate that the convention is to precede01b 01i 00 that is02i 02b 00 with a semicolon; however, among their examples are several in which it is preceded by an m-dash. They also state, interestingly, that it may be preceded by a comma if the following text is a phrase rather than a clause.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.