XML Schema for the GIR format

Hello,
I’d like to ask where I can find the XML Schema (XSD) for the format of the GObject introspection repository (GIR) files.
I’ve found the following file but that is in all likelihood not the schema.
Could somebody please point me in the right direction? Thanks a lot.

The gobject-introspection repository contains the GIR schema in RelaxNG form. It should be complete enough to validate the GIR files generated by g-ir-scanner.

Internet says that one should be able to transform the RelaxNG schema to XSD using trang

Thanks @ebassi