ISSUE-303: Incorrect note about language tag syntax

Incorrect note about language tag syntax

Raised by:
Addison Phillips
Opened on:

In Section 3.3 there is a note that reads:

Implementors might wish to note that language tags conform to the regular expression ’@’ [a-zA-Z]{1,8} (’-’ [a-zA-Z0-9]{1,8})* before normalizing to lowercase.

However, previously the spec required language tags to be "well-formed" by the rules in BCP47 section 2.2.9. The "well-formedness" requirement refers to the full ABNF syntax of language tags. The note's content is identical to the syntax of the "obs-language-tag" production in that same section of BCP47 (and intended for compatibility with older specs/implementations that referenced the obsolete RFC3066).

There is also no discussion of ASCII case-folding here. Depending on the locale or runtime configuration, some ASCII letters can casefold to non-ASCII values if this isn't specified.

I think your intention is clearly to encourage ASCII case-folding to lowercase.

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Related emails:
  1. I18N-ISSUE-303: Incorrect note about language tag syntax [.prep-RDF1.1] (from on 2013-10-10)

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Addison Phillips <>, Chair, Richard Ishida <>, Bert Bos <>, Fuqiao Xue <>, Atsushi Shimono <>, Staff Contacts
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