Case normalization of language tags in canonical form

[gkellogg]

Following on from w3c/rdf-concepts#74, if implementations have a choice (but are required to) case-normalize language tags, this allows for multiple canonical representations of the same triple/quad. We should consider requiring normalization to a specific form in canonicalization. If this normalization is not lower case, we risk breaking RDF Dataset Canonicalization.

[niklasl]

Makes sense, particularly when reading these from the note in https://www.w3.org/TR/rdf-canon/#introduction:

• The Canonicalization algorithm is based on the RDF 1.1 definition, in the sense that the language tag xx-YY is case insensitive, which might lead to different canonicalizations if the user is not aware of this problem.
• User communities ought to agree to use lower case language tags, while being aware that some implementations might normalize language tags, affecting hash values.
• Future evolution of RDF might regulate this issue, which RDF environments might have to adapt to, and this might lead to an update of RDFC-1.0.