A relatively recent development in the field of syntax envisages lexical items stored in the lexicon as catenae, whereby a given catena may or may not be a constituent.
A relatively recent development in the syntactic analysis of idioms departs from a constituent-based account of syntactic structure, preferring instead the catena-based account.
An alternative analysis of sluicing, and of multiple sluicing in particular, takes the catena (as opposed to the constituent of phrase structure grammars) as the fundamental unit of syntax.