I know that. It's still not a shibboleth: on the contrary, the meaning is so clear from the usage (except that one place in Romeo and Juliet), that any fluent speaker will recognize the meaning quickly even if they'd never seen it before. At best, it's a shibboleth for having watched any Shakespeare, but that's not what they meant to say.

There are many places in Shakespeare that are unreadable to a modern-English speaker without explanatory footnotes, but this isn't one of them.