Feat/rnc content-position annotations and non-leading start

[HassanAkbar]

Summary

• Parse bracket annotations in content positions without corrupting the tree
• Emit a real <start> for non-leading start = definitions
• Support combining starts: |= → choice, &= → interleave
• Keep an escaped \start as a regular define
• Require a comma between patterns in a sequence

[Copilot]

Pull request overview

This PR improves RELAX NG Compact (RNC) parsing and RNG XML emission around two tricky edge cases: bracket annotations that appear in “content positions” and start definitions that appear after other grammar items (including |=/&= combining starts).

Changes:

• Extend the RNC parser to skip bracket annotations before content items / definitions without capturing them into the parse tree, and tighten top-level sequence parsing to require commas.
• Update the RNC→RNG converter to emit a real <start> element for non-leading start = / start |= / start &= definitions (and preserve escaped \start as a normal <define>).
• Add advanced specs covering content-position annotations, non-leading start, combining starts, and escaped \start.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
spec/rng/advanced_rnc_spec.rb	Adds regression/feature specs for annotation-skipping and non-leading/combining start handling.
lib/rng/rnc_to_rng_converter.rb	Refactors start emission and adds detection/emission for non-leading start definitions.
lib/rng/rnc_parser.rb	Adds annotation_skip and uses it to drop content-position annotations; requires commas for top-level sequence items in pattern_list.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.