Step 3 is to test your declarations to make sure they work. This is simply a matter of creating an XML document that uses your local document type shell as its DTD and verifying that the @phase-of-moon attribute is now available on all elements that allow the selection attributes.

You can test the @domains declaration by trying to use the @phase-of-moon attribute for filtering or flagging. If the @domains attribute is not correctly specified, processors should either report that you have asked to flag or filter on an attribute that is not a specialization of @props or ignore the attribute completely and not do any filtering or flagging.