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| Dictionary | text | (optional) | The name of the external dictionary or external reference. |
| Version | text | (optional) | The version designator of the external codelist. |
| ref | text | (optional) | Reference to a local instance of the dictionary. |
| href | URI | (optional) | A resolvable URL to an external instance of the dictionary is preferred, however a non-resolvable URN, such as an OID or UUID, may be used. |
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