Slicing of DataElements is defined once per path (only one set of discriminators per unique path). This works for built-in elements, but extension is (and must be) sliced only by url. As a result, it appears that further (more detailed) slicing of an extension isn't possible.
For example, consider an extension to Patient for research authorizations, ext url "http://example.com/DataElement/researchAuth".
It has an extension sub-element "authorizationType" (http://example.com/DataElement/researchAuth.type) of type Code. Here are two instances of this extension (one type "local", one "national").
<extension url="http://example.com/DataElement/researchAuth">
<extension url="http://example.com/DataElement/researchAuth.type">
<valueCode value="local" />
</extension>
<extension url="http://example.com/DataElement/researchAuth.flag>
<valueBoolean value="true" />
</extension>
</extension>
<extension url="http://example.com/DataElement/researchAuth">
<extension url="http://example.com/DataElement/researchAuth.type">
<valueCode value="national" />
</extension>
<extension url="http://example.com/DataElement/researchAuth.flag>
<valueBoolean value="false" />
</extension>
</extension>
The StructureDefinition for this would include (from Patient):
...snip...
<element>
<path value="Patient.extension" />
<slicing>
<discriminator value="url" />
</slicing>
</element>
I could add an element for researchAuthorization by using type.Profile to define the extension URL, but can I add a slicing as shown?
<element>
<path value="Patient.extension" />
<slicing>
<discriminator value="url" />
</slicing>
</element>
<element>
<path value="Patient.extension" />
<name value="researchAuthorization" />
<slicing>
<discriminator value="url" />
<discriminator value="extension["http://example.com/DataElement/researchAuth.type"].code" />
</slicing>
<type>
<profile value="http://example.com/DataElement/researchAuth" />
</type>
</element>
The second is now legal since it "satisfies" the first slicing via type.profile.@value being fixed?
