Clarification for user_id and user_id_type

[Nicolas Aillery]

Clarification on the presence of user_id in the User Statement Token:

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The <spanx style="verb">user_id</spanx> is present in the User Statement Token only if the <spanx style="verb">user_id</spanx> and <spanx style="verb">user_id_type</spanx> were present in the User Questioning Request. 
+
The <spanx style="verb">user_id</spanx> MUST be present in the User Statement Token if, and only if, the <spanx style="verb">user_id</spanx> and <spanx style="verb">user_id_type</spanx> were present in the User Questioning Request. 

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Clarification on the presence of user_id_type in the User Statement Token:

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OPTIONAL. The <spanx style="verb">user_id_type</spanx> is present in the User Statement Token only if the <spanx style="verb">user_id</spanx> and <spanx style="verb">user_id_type</spanx> were present in the User Questioning Request.
+
OPTIONAL.
The <spanx style="verb">user_id_type</spanx> MUST be present in the User Statement Token if, and only if, the <spanx style="verb">user_id</spanx> and <spanx style="verb">user_id_type</spanx> were present in the User Questioning Request.

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[Bjorn Hjelm]

Approved.