appositive or ellipsis

Stripping is also known as bare argument ellipsis. Many linguists take stripping to be a particular manifestation of gapping whereby just one remnant appears in the gapped clause instead of the two (or more) that occur in instances of gapping. The fact that stripping is limited to occurring in coordinate structures is the main reason why stripping is integrated into the analysis of gapping:

John can play the guitar, and Mary can play the guitar, too. - Stripping
Sam has attempted problem 1 twice, and he has attempted problem 2 also. - Stripping

These examples illustrate that stripping is flexible insofar as the remnant in the stripped clause is not limited in function; it can, for instance, be a subject as in the first sentence or an object as in the second sentence. A particularly frequent type of stripping is not-stripping, e.g.

Sam did it, not Fred. - not-Stripping
Sally is working on Monday, not on Tuesday. - not-Stripping

Not-stripping's status as a form of ellipsis can be debated, since the non-elliptical versions of these sentences are unacceptable. The key trait of ellipsis, namely, is that the both versions are supposed to be acceptable (the elliptical and non-elliptical version).