Contradiction in TraceState format description

[xrfang]

Section 3.3.1.3.1 Key says:

The key identifies the tracestate entry.

key = simple-key / multi-tenant-key
simple-key = lcalpha 0255( lcalpha / DIGIT / "_" / "-"/ "" / "/" )
multi-tenant-key = tenant-id "@" system-id
tenant-id = ( lcalpha / DIGIT ) 0240( lcalpha / DIGIT / "_" / "-"/ "" / "/" )
system-id = lcalpha 013( lcalpha / DIGIT / "_" / "-"/ "" / "/" )
lcalpha = %x61-7A ; a-z

Note: Identifiers MUST begin with a lowercase letter or a digit, and can only contain lowercase letters (a-z), digits (0-9), underscores (_), dashes (-), asterisks (*), and forward slashes (/).

The ABNF mandates that simple-key must start with lcalpha, but the note says identifiers can be either a lower case letter and a DIGIT.

url of the document: https://www.w3.org/TR/trace-context/#key

[basti1302]

Right, that wording of the note is not optimal. IIRC, the intention was that simple keys MUST start with a letter (not with a digit) while multi-tenant keys can start either with an lcalpha or with a digit. That is what the ABNF expresses, and I think that is correct.

Either way, note that the latest version of the spec has already rectified this issue, doing away with the distinction between simple keys and multi-tenant keys: https://w3c.github.io/trace-context/#list-members, so I don't think there is an action item here.

For implementers, my personal suggestion would be to already go with ABNF from the latest version.

For the record, this is where the simplification of the ABNF has been discussed: #386 -- the main change being that @ is not given any special meaning anymore.