This is the repository that contains the RelaxNG schema that is part of the EDXML Specification.
The schema can be used in your projects by cloning this repository. For PHP and Python projects you can also use a package manager to add the schema as a dependency. This repository includes both a Python package and a Composer package for PHP.
Both the Python and PHP packages are distributed using the MIT license. The actual RelaxNG schema file, which is included in both packages, uses a Creative Commons license as indicated in the schema itself.