=item * Unknown command "I<CMD>"
An invalid POD command has been found. Valid are C<=head1>, C<=head2>,
-C<=over>, C<=item>, C<=back>, C<=begin>, C<=end>, C<=for>, C<=pod>,
-C<=cut>
+C<=head3>, C<=head4>, C<=over>, C<=item>, C<=back>, C<=begin>, C<=end>,
+C<=for>, C<=pod>, C<=cut>
=item * Unknown interior-sequence "I<SEQ>"
'cut' => 1,
'head1' => 1,
'head2' => 1,
+ 'head3' => 1,
+ 'head4' => 1,
'over' => 1,
'back' => 1,
'item' => 1,
=head1 heading
=head2 heading
+ =head3 heading
+ =head4 heading
=item text
=over N
=back
=item =head2
-Head1 and head2 produce first and second level headings, with the text in
-the same paragraph as the "=headn" directive forming the heading description.
+=item =head3
+
+=item =head4
+
+Head1, head2, head3 and head4 produce first, second, third and fourth
+level headings, with the text in the same paragraph as the "=headn"
+directive forming the heading description.
=item =over