If Header interaction with If-Match, etc

What, if any, interaction does the If header have with the other 
conditional headers?  HTTPbis part 4 
(http://tools.ietf.org/html/draft-ietf-httpbis-p4-conditional) 
specifically states which headers can't/shouldn't be used together.

I assume that If-Match and If-None-Match shouldn't be used with If, but 
what about If-[un]modified-Since and If?  Should an implementation just 
look for and use If when specified and ignore all other conditionals?

-- 
Kenneth Murchison
Principal Systems Software Engineer
Carnegie Mellon University