What will browser show when a user access website and website present certificate of some other domain with same top level domain For example, User tries to access a.example.com and server presents abc.example.com with a.example.com not in SANs list.
Will it be just a warning or an error?
A well designed browser should display a warning page whenever there is a problem with a certificate for the asked paged.

Firefox and Chrome will provide a way to manually bypass the page.