-Currently only one subpragma, C<access> is implemented. It enables
-(or disables) the use of access() or similar system calls. This
-extended filetest functionality is used only when the argument of the
-operators is a filename, not when it is a filehandle.
+Because access() does not invoke stat() (at least not in a way visible
+to Perl), B<the stat result cache "_" is not set>. This means that the
+outcome of the following two tests is different. The first has the stat
+bits of F</etc/passwd> in C<_>, and in the second case this still
+contains the bits of C</etc>.
+
+ { -d '/etc';
+ -w '/etc/passwd';
+ print -f _ ? 'Yes' : 'No'; # Yes
+ }
+
+ { use filetest 'access';
+ -d '/etc';
+ -w '/etc/passwd';
+ print -f _ ? 'Yes' : 'No'; # No
+ }
+
+Of course, unless your OS does not implement access(), in which case the
+pragma is simply ignored. Best not to use C<_> at all in a file where
+the filetest pragma is active!
+
+As a side effect, as C<_> doesn't work, stacked filetest operators
+(C<-f -w $file>) won't work either.
+
+This limitation might be removed in a future version of perl.