... nor can forms ?

Invariant or non-finite forms, such as be in You have to be good can’t be deleted, nor can forms that are stressed (He is tall) or that come at the end of a clause (That’s what he is).

Hello, everyone.
What is the meaning of “nor can forms” in the sentence above? I wonder why is ‘forms’, isn’t ‘form’? What part of speech is ‘form’ here?
Because ‘forms’ follows ‘can’. So I think ‘forms’ should be a Verb.
I found that sentence in ‘American Heritage Dictionary’, while looking for the meaning of ‘zero copula’.
Anyway thanks in advance.

You are combining the words incorrectly. That does not refer to a ‘nor can’ form.
nor=neither
forms is a noun.
The writer means that forms which are stressed or come at the end of a clause can’t be deleted either.