A little discussed feature of English are non-restrictive relative clauses in which the antecedent is normally not an NP and the gap follows an auxiliary, as in Kim will sing, which Lee won?t. These relative clauses resemble clauses with auxiliary complement ellipsis or fronting. There are a variety of analyses that might be proposed, but there are reasons for thinking that the best analysis is one where which is a nominal filler associated with a gap which is generally non-nominal: a filler-gap mismatch analysis in other words
