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!