Primitive type 'url'
A telecommunications address specified according to Internet standard RFC 1738 [http://www.ietf.org/rfc/rfc1738.txt]. The URL specifies the protocol and the contact point defined by that protocol for the resource. Notable uses of the telecommunication address data type are for telephone and telefax numbers, e-mail addresses, Hypertext references, FTP references, etc.
All FHIR elements must have a @value or children
hasValue() or (children().count() > id.count())
unique id for the element within a resource (for internal references)
Must have either extensions or value[x], not both