The online help manual for Roundcube is available as a HTML package that can also be embedded into the help plugin for inline display within the webmail application. It's written in the reStructuredText (reST) format and generated using the Sphinx Documentation Generator.

You can find the sources as well as guidance on how to build and extend the online help in a dedicated github repository.

The help documents are available online at https://docs.roundcube.net/.

Note: the documentation is not complete yet! Contributions are much appreciated.