Why is there so little documentation for ProjectSchemaDefinitions?

[msedi]

We are delivering an msbuild task via nuget. The task is to compile and create CUDA C# wrappers and the necessary additional modules.
Since CUDA files and the create files do not fit into the regular content types we have created our own content types by using the ProjectSchemaDefinitions and the PropertyPageSchema but it is pretty hard to get this right because there is almost no docs for htis.

Is it still valid to use this, or do we need to do it differently?