alias
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... names are assigned a single primary name for the charset MUST be
identified. All other names are considered to be aliases for the
primary name and use of the primary name is preferred over use of any
of the aliases ...
... aliases for the
primary name and use of the primary name is preferred over use of any
of the aliases.
...
... charset. If no name of this form is
explicitly defined IANA will assign an alias consisting of "cs"
prepended to the primary charset name.
...
... aliases:
(All aliases must also be suitable for use as the value of
a MIME content-type parameter.)
...