__END__
+=method next_version_set
+
+ while (my $version_set = $versions->next_version_set) {
+ ...
+ }
+
+=method previous_version_set
+
+ while (my $version_set = $versions->previous_version_set) {
+ ...
+ }
+
# normally a VersionHandler will take
# a to_version and yeild an iterator of
# "version sets" or something like that.