Is there a schema (preferably commented) for concrete5-cif anywhere? That would be good documentation.
A proper schema would also provide a way to verify that whatever you end up putting together if you do it from scratch is syntactically and semantically correct, using common xml tools.
First of all, it’s still a work in progress, I think I’ll reach an usable version in a week or two.
Second, given the complexity of Concrete CIF files, XSD 1.0 is not enough: we need 1.1.
The problem is that 1.1 is not supported by PHP and many IDEs (VSCode Eclipse, … not sure about others).
And the only open source library that supports 1.1 seems to be Xerces (and for this reason the project above also comes with a Java program you can use to check CIF files).