The SubdomainOf function tests whether one domain is a subdomain of another specified domain.
Returns true if uri is a subdomain of uriTemplate; false if it is not.
Parameter values must include the scheme portion of the URI, for example "sip:firstname.lastname@example.org".
For SIP URIs (URIs that begin with "sip:" or "sips:"), this function performs a postfix match on the domain. For example, "test.msn.com" is identified as a subdomain of "msn.com".
The wildcard character ("*") and regular expressions are not supported.