invoke.texi (-Wformat): Document what format features are checked.

	* invoke.texi (-Wformat): Document what format features are
	checked.

From-SVN: r38103

gcc/ChangeLog

+2000-12-07  Joseph S. Myers  <jsm28@cam.ac.uk>
+
+	* invoke.texi (-Wformat): Document what format features are
+	checked.
+
 2000-12-06  Kazu Hirata  <kazu@hxi.com>
 
 	* config/h8300/h8300.h: Fix formatting.

gcc/invoke.texi

@@ -1598,6 +1598,16 @@ Check calls to @code{printf} and @code{scanf}, etc., to make sure that
 the arguments supplied have types appropriate to the format string
 specified.
 
+The formats are checked against the format features supported by GNU
+libc version 2.2.  These include all ISO C89 and C99 features, as well
+as features from the Single Unix Specification and some BSD and GNU
+extensions.  Other library implementations may not support all these
+features; GCC does not support warning about features that go beyond a
+particular library's limitations.  However, if @samp{-pedantic} is used
+with @samp{-Wformat}, warnings will be given about format features not
+in the selected standard version.  @xref{C Dialect Options,,Options
+Controlling C Dialect}.
+
 @samp{-Wformat} is included in @samp{-Wall}.  For more control over some
 aspects of format checking, the options @samp{-Wno-format-y2k},
 @samp{-Wno-format-extra-args}, @samp{-Wformat-nonliteral} and