Need reference to good ABNF for \uXXXX syntax

[Doug Ewell]

Is anyone aware of an existing RFC or other specification that includes complete, correct, and clear ABNF for Unicode escape sequences using the UTF-16 encoding scheme?

Examples:
\u0041
\u3042
\uD801\uDC02  (NOT: \U0001042A)

This type of sequence is described in Section 6.3 of RFC 5137, but that RFC does not recommend this syntax and does not include ABNF for it.

"Correct" implies, for instance, that the ABNF excludes unpaired surrogates.

To be clear, I'm NOT looking for someone on this list to contribute their own code, but rather a pointer to code that is already published, and easy for another document, such as an I-D, to reference.

--
Doug Ewell, CC, ALB | Lakewood, CO, US | ewellic.org