Creating and importing a classification schema

Where would the best place be to get more information/learning for creating and importing classifiers?
I’ve gone through the classifying objects article at https://help.sketchup.com/en/article/3000128
But there was very little in the way of creating a new one.

I also tried the example it had and made the same changes it said to do and when i tried to import it i got an error message: Sketchup could not load the following classification system files for an unknown reason: TestSchema.skc

So any nudge in the right direction would be helpful.

Because you must understand XML and how to define a schema (using the XSD language,) for a custom XML format.

There are references out on the web:
https://www.w3.org/standards/xml/

It is not Trimble’s job, nor mission, to teach web programming languages.