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<h4 class="subsection">1.2.5 XPG (The X/Open Portability Guide)</h4>

<p>The X/Open Portability Guide, published by the X/Open Company, Ltd., is
a more general standard than POSIX.  X/Open owns the Unix copyright and
the XPG specifies the requirements for systems which are intended to be
a Unix system.

   <p>The GNU C library complies to the X/Open Portability Guide, Issue 4.2,
with all extensions common to XSI (X/Open System Interface)
compliant systems and also all X/Open UNIX extensions.

   <p>The additions on top of POSIX are mainly derived from functionality
available in System&nbsp;V<!-- /@w --> and BSD systems.  Some of the really bad
mistakes in System&nbsp;V<!-- /@w --> systems were corrected, though.  Since
fulfilling the XPG standard with the Unix extensions is a
precondition for getting the Unix brand chances are good that the
functionality is available on commercial systems.

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