requirement
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With the international Internet follows an absolute requirement to
interchange data in a multiplicity of languages, which in turn
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... charsets, or even using a default other
than UTF-8, may be a requirement. This is acceptable, but UTF-8
support MUST be possible.
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... Requirement for language tagging ...
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Note that this does NOT mean that such information must always be
present; the requirement is that if the sender of information wishes
to send information about the language ...
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Negotiating a language should be regarded as a permanent requirement
of the protocol that will not go away at any time in the future.
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... Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. ...