A preprocessing directive of the form
(that does not match one of the two previous forms) is permitted.
The preprocessing tokens after
in the directive are processed just as in normal text
(i.e., each identifier currently defined as a macro name is replaced by its
replacement list of preprocessing tokens).
If the directive resulting after all replacements does not match
one of the two previous forms, the behavior is
The method by which a sequence of preprocessing tokens between a
preprocessing token pair or a pair of
characters is combined into a single header name
preprocessing token is implementation-defined.