19.2.2.3 Restrictions on Wildcard Pathnames

Wildcard pathnames can be used with directory but not with open, and return true from wild-pathname-p. When examining wildcard components of a wildcard pathname, conforming programs must be prepared to encounter any of the following additional values in any component or any element of a list that is the directory component:

* The symbol :wild, which matches anything.

* A string containing implementation-dependent special wildcard characters.

* Any object, representing an implementation-dependent wildcard pattern.