Functions, headers, and external variables that comprised the Legacy Feature Group in Single UNIX Specification, Version 2 are removed and not part of SUSv3. Also, any symbols that were marked obsolescent in Version 2 have been removed.
For a complete list of the withdrawn symbols, see the description of _UNIX03_WITHDRAWN in Feature Test Macros in z/OS XL C/C++ Runtime Library Reference. In the case of headers that have been withdrawn, there is no special mechanism employed. An application simply includes them, like any other non-standard header. The withdrawn headers are <re_comp.h>, <regexp.h>, and <varargs.h>. Dependencies on symbols that are not part of the SUSv3 namespace affect portability and, if this is an issue, make such applications nonconforming.