VMS Help CC, /NESTED_INCLUDE_DIRECTORY  *Conan The Librarian (sorry for the slow response - running on an old VAX)

     /NESTED_INCLUDE_DIRECTORY[=option]
     /NESTED_INCLUDE_DIRECTORY=INCLUDE_FILE (D)

  Controls the first step in the search algorithm the compiler uses
  when looking for files included using the quoted form of the
  #include preprocessing directive:  #include "file-spec"

  /NESTED_INCLUDE_DIRECTORY has the following options:

  PRIMARY_FILE   Directs the compiler to search the default file type
                 for headers using the context of the primary source
                 file (the .C file).  This means that just the file
                 type (".H" or ".") is used for the default file-spec
                 but, in addition, the chain of "related file-specs"
                 used to maintain the sticky defaults for processing
                 the next top-level source file is applied when
                 searching for the include file.

  INCLUDE_FILE   Directs the compiler to search the directory
                 containing the file in which the #include directive
                 itself occurred.  The meaning of "directory
                 containing" is:  the RMS "resultant string" obtained
                 when the file in which the #include occurred was
                 opened, except that the filename and subsequent
                 components are replaced by the default file type for
                 headers (".H", or just "." if
                 /ASSUME=NOHEADER_TYPE_DEFAULT is in effect).  The
                 "resultant string" will not have translated any
                 concealed device logical.

  NONE           Directs the compiler to skip the first step of
                 processing #include "file.h" directives.  The
                 compiler starts its search for the include file in
                 the /INCLUDE_DIRECTORY directories.

  See also /INCLUDE_DIRECTORY.