Rational Publishing Engine allows drilling into the class, the class attributes, and the types of those attributes. Then the Rational Publishing Engine schema starts referring to nested elements and nested elements do not have types that can be drilled into.
The schema defines the relation, which represents a Classifier. Classifier is the base type for all of the possible types an attribute can have.
To make the second query example valid, you must split it in two queries:
Container element
into the template content editor.
Cast to Type icon
to add the Class type cast for the ownedMember.
Paragraph element below
the container element.