scalar ((C<< $ >>), array (C<< @ >>) and hash (C<< % >>) prefix sigils
+Check that the C<< + >> postfix sigil works, that numbers can default to
+values other than zero, and that an explicit C<isa> works.
+Make sure that sigils are just hints, and can be overridden by an explicit
+Checks that attribute specs can be hashrefs or arrayrefs.
Toby Inkster E<lt>firstname.lastname@example.orgE<gt>.