A valid ref spec is a string that starts 
with the literal 'element ', and is followed by

* Either a star '*' OR by m/-dir(ectory)? \S+/
                    OR by m/-file \S+/
* then by a label

A label is ...

##</code><code>##

my $re = qr{
   element \s
      (
        \*
      | -dir(ectory)? \S+
      | -file \S+
      )
   # Label:
   \w+
}x;