s9e\TextFormatter is a text formatting library that supports BBCode, Markdown, HTML and other markup via plugins. The library is written in PHP, with a JavaScript port also available for client-side preview (see below.)
The best way to install s9e\TextFormatter is via Composer. See Installation.
composer require s9e/text-formatter
If you can only read one example, read how to use a bundle.
You can run the scripts directly from the examples directory and you will find in the manual a description of each plugin as well as other examples.
Versioning is meant to follow Semantic Versioning. You can read about API changes in the documentation.
You can try the JavaScript version in this BBCodes + other stuff demo, or this Markdown + stuff (Fatdown) demo.