This is a HL7 FHIR server, and as you appear to be accessing this page from a web browser you are seeing a HTML version of the requested resource(s). You can also access this URL from a FHIR client as a ReSTful API call. For more details please see the HL7 FHIR specification.
<?xml version="1.0" encoding="UTF-8" standalone="no"?><NamingSystem xmlns="http://hl7.org/fhir">
   <name value="NHS Number"/>
   <status value="draft"/>
   <kind value="identifier"/>
   <date value="2015-05-01"/>
   <publisher value="NHS Digital"/>
   <contact>
      <name value="Interoperability Team"/>
      <telecom>
         <system value="email"/>
         <value value="interoperabilityteam@nhs.net"/>
         <use value="work"/>
      </telecom>
   </contact>
   <responsible value="NHS Digital"/>
   <description value="NHS Number allocated to the patient."/>
   <usage value="A unique patient identifier for everyone registered with the NHS."/>
   <uniqueId>
      <type value="uri"/>
      <value value="https://fhir-test.hl7.org.uk/Id/nhs-number"/>
      <preferred value="true"/>
   </uniqueId>
   <uniqueId>
      <type value="oid"/>
      <value value="2.16.840.1.113883.2.1.4.1"/>
      <preferred value="false"/>
   </uniqueId>
</NamingSystem>