How does a caching relay handle different unknown extensions? #1380
Description
The text currently says:
Object Header Extensions can be added, removed or updated, subject to the constraints of the specific header extension.
However, if a cache doesn't support the extension, then it has no idea what the constraints are and we need to specify a default behavior.
The question also applies to Track level extensions in #1374.
I think the only reasonable behavior might be append and resolve duplicates:
A=B + A=C = {A=B, A=C}
A=B + empty = {A=B}
A=B + A=B = {A=B}