Modification: Unless the transplant involves identical twins

[imported_n/a]

I am unsure of modification and what the clause or phrase sometimes modifies.

Unless the transplant involves identical twins who have the same genetic endowment, all patients receiving hearts, etc. etc.

How can the transplant involves identical twins who have the same genetic endowment etc. etc. describe all patients and the sentence still be correct. Is it because if the clause has no action or adjective any modification is correct? ?

[Erin]

Modifiers are words or phrases that modify other words, phrases, or sentences. What you think is a modifier here is actually a clause:

Unless the transplant involves identical twins who have the same genetic endowment

Most clauses (i.e., full clauses, not reduced clauses) do not follow the rules that govern dangling modifiers, and this one is not an exception.