perldiag: note the exceptions for "once" warnings

diff --git a/pod/perldiag.pod b/pod/perldiag.pod
index 6552f67..a6c105c 100644 (file)
--- a/pod/perldiag.pod
+++ b/pod/perldiag.pod
@@ -3127,7 +3127,9 @@ provided for this purpose.
 NOTE: This warning detects symbols that have been used only once so $c, @c,
 %c, *c, &c, sub c{}, c(), and c (the filehandle or format) are considered
 the same; if a program uses $c only once but also uses any of the others it
-will not trigger this warning.
+will not trigger this warning.  Symbols beginning with an underscore and
+symbols using special identifiers (q.v. L<perldata>) are exempt from this
+warning.
 
 =item Need exactly 3 octal digits in regex; marked by <-- HERE in m/%s/