It's not the case that all CQL will exist at the 'root' of the Questionnaire.  Some CQL will exist in various layers of the Questionnaire and context is driven by where within the Questionnaire the CQL is defined.  Definitions for CQL appearing on an item are available for descendant items, but not sibling items.  As well, the 'name' elements of the Expressions come into play.  SDC doesn't cover this aspect of CQL that well - in large part because most SDC implementations strictly use FHIRPath, not CQL.  So additional guidance here would be helpful.  But the guidance provided is not sufficient.

Finally, this section shouldn't be making reference to CQF, but rather to SDC.  And there's no such thing in either CQF or SDC as "valueExpression".