In an ODD, Schematron rules, assertions, or reports can appear in a constraintSpec
scheme="isoschematron" which itself can appear in attDef,
classSpec, elementSpec, or schemaSpec.
If the sch:rule is missing (i.e., just bare sch:assert and
sch:report elements), then the context is the element or attribute that is
being defined.
In an ODD, you need to specify the tei: prefix for TEI elements!