isWildcard

Whether this variable follows the wildcard naming convention, i.e. whether its name starts with "_" (e.g. _, _P, _Foo). Broader than isAnonymous (which only matches "_" exactly): unlike a true anonymous variable, a named wildcard like _P can still be meaningfully shared across occurrences within a clause -- the convention only means "the user doesn't care to see its value", not "never shared".