CommonMark

CommonMark is a robust, highly-extensible Markdown parser PHP library. It is based on the CommonMark specification. 

Markdown syntax is lightweight markup language. Many different "flavors" of Markdown have been developed with limited consistency due to the lack of an official specification. The CommonMark specification attempts to solve this problem by providing a single specification that various Markdown parsers can utilize.

The CommonMark parser was developed as a PHP library that adheres to the CommonMark specification. It was designed to be extensible, and easy-to-use API. Out-of-the box, it is fully compatible with the CommonMark specification as well as the widely-used Github-Flavored Markdown specification (which adds some extensions to the CommonMark specification.