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Registry included below
| Token | Description | Reference |
|---|---|---|
| unknown | The number's semantics are unknown. This value is the default in the absence of this parameter. | [RFC3939] |
| local | The number only has meaning within the domain of the sending system identified by the [RFC2822] From field of the message. | [RFC3939] |
| e164 | The number's semantics are described in [ITU-T Recommendation E.164 (1997), "The international public telecommunication numbering plan"]. | [RFC3939] |