perlvar: Document ${^WARNING_BITS} better

Don’t refer people to warnings.pm for more information, as it
contains no more information about this variable.

Explain the scoping and also mention that the values are
considered internal.

diff --git a/pod/perlvar.pod b/pod/perlvar.pod
index 3ae354c..f7dbfbb 100644 (file)
--- a/pod/perlvar.pod
+++ b/pod/perlvar.pod
@@ -1622,7 +1622,9 @@ Mnemonic: related to the B<-w> switch.
 X<${^WARNING_BITS}>
 
 The current set of warning checks enabled by the C<use warnings> pragma.
-See the documentation of C<warnings> for more details.
+It has the same scoping as the C<$^H> and C<%^H> variables.  The exact
+values are considered internal to the L<warnings> pragma and may change
+between versions of Perl.
 
 This variable was added in Perl 5.10.