FEATURE: Leaf Block Parser

Scope

The parser recognizes CommonMark 0.31.2 leaf blocks:

• thematic breaks;
• ATX headings;
• setext headings;
• indented code blocks;
• fenced code blocks;
• HTML blocks;
• paragraphs;
• link reference definitions.

Leaf parsing occurs before inline parsing. Link reference definitions are collected for later resolution and do not render as visible blocks.

Programmatic Acceptance

Suite: scoped
Requires: executable=python3; scope=test

=== AC leaf-blocks-primary ===
Intent: The implementation passes the supplied conformance sections for thematic breaks, headings, and code blocks.

import subprocess import sys

result = subprocess.run( [ sys.executable, "spec_tests.py", "--spec", "spec.txt", "--program", "./cmark", "--pattern", "Thematic breaks|ATX headings|Setext headings|Indented code blocks|Fenced code blocks", ], capture_output=True, text=True, ) print(result.stdout) print(result.stderr, file=sys.stderr) assert result.returncode == 0 === END AC leaf-blocks-primary ===

=== AC leaf-blocks-secondary ===
Intent: The implementation passes the supplied conformance sections for HTML blocks, link references, paragraphs, and blank lines.

import subprocess import sys

result = subprocess.run( [ sys.executable, "spec_tests.py", "--spec", "spec.txt", "--program", "./cmark", "--pattern", "HTML blocks|Link reference definitions|Paragraphs|Blank lines", ], capture_output=True, text=True, ) print(result.stdout) print(result.stderr, file=sys.stderr) assert result.returncode == 0 === END AC leaf-blocks-secondary ===

User Acceptance

• None.

Guardrails

• Leaf blocks are parsed before inline constructs.
• Code blocks preserve literal content and do not parse inline syntax.
• Link reference definitions are not emitted as visible HTML blocks.
• Verification uses the supplied harness with selectors that match example-bearing sections.