Detailed Specifications
Pulldown-cmark's test suite follows the convention, set by CommonMark itself, of writing specifications that double as conformance tests.
The CommonMark Specification is copied from https://spec.commonmark.org, but slightly modified because pulldown-cmark and cmark don't escape special characters in the exact same way (though their results are identical when rendered with a web browser).
The "GitHub" specifications have been excerpted from https://github.github.com/gfm/.