Attribute citation

[T0mstone]

From what I've seen, only the docstring of LanguageTag itself includes a portion of RFC 5646 verbatim.

License-wise, this is probably not ok. RFC 5646 states at the beginning:

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info).

Given that it was published in september 2009, I had a look at the Trust Legal Provisions 3.0 from Sept 12, 2009. The relevant portion here is

[3.c]. Licenses For Use Outside the IETF Standards Process. In addition to the rights granted with respect to Code Components described in Section 4 below, the IETF Trust hereby grants to each person who wishes to exercise such rights, to the greatest extent that it is permitted to do so, a non-exclusive, royalty-free, worldwide right and license under all copyrights and rights of authors:   iii. to copy, publish, display and distribute unmodified portions of IETF Contributions and IETF Documents and translations thereof, provided that:     (x) each such portion is clearly attributed to IETF and identifies the RFC or other IETF Document or IETF Contribution from which it is taken,     (y) all IETF legends, legal notices and indications of authorship contained in the original IETF RFC must also be included where any substantial portion of the text of an IETF RFC, and in any event where more than one-fifth of such text, is reproduced in a single document or series of related documents.

Since (from what I can tell) documentation doesn't count as Code Components, you need to attribute that portion of the RFC properly. (I'm pretty sure that that single paragraph isn't a substantial portion, so (y) probably doesn't apply.)

Of course, the paragraph does come after a link to the original document, which could maybe be seen as enough, but, at least to me, it wasn't obvious that that paragraph was a citation before I looked it up.

Disclaimer: I am not a lawyer and am only going off my layman's understanding obtained from simply reading the legal documents.