Returns a node-set of member groups (roles) that have access to the restricted content document.
umbraco.library:AllowedGroups(int documentId, string path)
An example of the returned XPathNodeIterator (as XML):
<roles>
<role>1050</role>
<role>1066</role>
<role>1072</role>
</roles>
The value of the <role> are the Id of the Member Group.