No, I was actually trying to be specific. There's usually nothing wrong with 0/1 or 1-9.

Empirically, 0/1/2 either means no/yes/yes-and-something-obscure-on-top-of-that, or, worse, as in this case, no/kind-of-but-not-really/yes.

It's akin to http://c2.com/cgi/wiki?ZeroOneInfinityRule. If you started out thinking it was just a switch, you should be very reluctant to add a third state without rethinking what you really need to express, or you end up with my favorite from TheDailyWTF:

  enum Bool { 
      True,
      False,
      FileNotFound
  };

This would have been much safer as separate AUTHENTICATE_CERT (which checks the CA sig and expiry and revocation) and VERIFY_CERT_COMMON_NAME options, both of which default to true.

Your more general adage is useless. The one you responded to is useful. A more useful, also general adage would be "the more choice in selecting parameters to an API, the more likely there will be bugs consuming that API."