Potential issues with ABNF description

[henkbirkholz]

chapters/external-repository-identifiers.md does not read quite right to me. I checked with @cabo and there might be a few issues with this ABNF definition:

• 'idstring' can start with a "-". Is that intentional? That looks curious.
• 'compound-expression' has undefined operator precedence (wrt WITH, AND, and OR)
• While "DocumentRef-" and "LicenseRef-" are expressed in UpperCamelCase, they are case-insensitive. Is that intentional?
  • use %s and reference RFC7405, if case-sensitive was intended
• introduce and explain that ALPHA and DIGIT from RFC 5234
• 'license-expression' is redundant: 'compound-expression' already includes 'simple-expression'

Additionally, the ABNF included does not really parse. Here is a proper one:

idstring = 1*(ALPHA / DIGIT / "-" / "." )

license-id = <short form license identifier in Annex A.1>

license-exception-id = <short form license exception identifier in Annex A.2>

license-ref = ["DocumentRef-" (idstring) ":"] "LicenseRef-" (idstring)

simple-expression = license-id / license-id "+" / license-ref

compound-expression = (simple-expression /
  simple-expression "WITH" license-exception-id /
  compound-expression "AND" compound-expression /
  compound-expression "OR" compound-expression /
  "(" compound-expression ")" )

license-expression = (simple-expression / compound-expression)

[zvr]

@henkbirkholz your link goes to #658. Is this intentional?

[zvr]

If this is about license expression grammar, then we should continue on #456 which was opened almost two years ago.

[kestewart]

This was resolved in #474. If you disagree @henkbirkholz - please reopen.