Compliance

Alto separates language compliance from safe application rendering. The parser profiles define accepted syntax, while HtmlPolicy defines output safety.

Supported specifications

The CommonMark and GFM profiles are checked against pinned specification examples. GitHub-specific fixtures cover alerts, front matter, safe HTML, and direct versus document rendering parity.

HtmlPolicy::spec() is used by conformance tests because raw HTML passthrough belongs to the specifications. Normal application rendering remains safe by default.

Run the suites

The published package carries the conformance fixtures and runs them with the rest of the suite:

composer tests

The full quality gate also runs static analysis and style checks on top of the unit, integration, source-preservation, round-trip, lint, formatter, and file-save tests:

composer qa

Interpret guarantees

Alto verifies three different properties:

• Conformance: HTML matches the selected specification examples.
• Semantic round-trip: normalized Markdown reparses to an equivalent model.
• Source preservation: unchanged or unrelated input bytes are not rewritten.

These guarantees apply only to the selected profile. A GitHub extension such as an alert is ordinary blockquote content under narrower profiles. Opt-in syntax such as description lists, footnotes, tabs, constrained attributes, and recursive includes and embeds is outside the CommonMark and GFM conformance score. Render-only output such as heading sections is also outside those specification scores. Each extension has separate direct-render, document-render, and source-preservation tests.