Existing Wording: Example:

<Patient xmlns="http://hl7.org/fhir">
<extension url="http://hl7.org/fhir/StructureDefinition/patient-clinicalTrial">
<extension url="http://hl7.org/fhir/StructureDefinition/patient-clinicalTrialNCT">
<valueString value="NCT01647425"/>
</extension>
<extension url="http://hl7.org/fhir/StructureDefinition/patient-clinicalTrialPeriod">
<valuePeriod>
<start value="2012-04-01"/>
<end value="2013-09-30"/>
</valuePeriod>
</extension>
<extension url="http://hl

FHIR resource in XML serialized form can be complex especially if it contains extensions of structured (type=Element) which is implemented as extensions of extensions.

Some examples were created using the full absolute URL for all extension elements but the sub-elements such be inferred by its context within the root extension. FHIR Documentation in section 1.16.0.1 show an example with sub-element extensions with only part URL identifier (e.g. url="code", url="date", etc.) but the target extension http://acme.org/fhir/StructureDefinition/trial-status is not a real extension so cannot examine the extension definition nor validate if an extension actually follows the extension definition.

In theory, a valid example could be rewritten with partial url for the sub-elements:

<Patient xmlns="http://hl7.org/fhir">
<extension url="http://hl7.org/fhir/StructureDefinition/patient-clinicalTrial">
<extension url="clinicalTrialNCT">
<valueString value="NCT01647425"/>
</extension>
...

Need example of nested extensions of actual extension in FHIR.