RFC 3958:Domain-Based Application Service Location...
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... Starting with the first sorted NAPTR record, the client examines the ...
... That is, the client MUST NOT start looking for one protocol, observe that a successive NAPTR RR ...


... app-protocol tags are limited to 32 ; characters and must start with an alphabetic character. ; The service-parms are considered case-insensitive ...


... All application service and protocol tags that start with "x-" are considered experimental, and no provision is made to prevent ...



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