Return the pathname class defined for the given pathname scheme, otherwise return nil. A pathname namestring may include a scheme or logical host prefix ending with a colon, and this prefix is used by parse-namestring to determine the pathname class before parsing the namestring. The common URI schemes are defined and return the class pathname: file, http, https, ftp, and telnet. The pathname class for other schemes may be defined using (setf scheme-pathname-class). Logical pathnames have a separate namespace.

Set the pathname class associate with the pathname scheme. This is used by make-pathname, and parse-namestring to select the pathname class.