Describes the intended purpose of the rendered text. For example - instructions, guidance on access control, maintenance information, etc. ... Context of Use: Use on Element ID Questionnaire.item or Element ID Questionnaire.item.item, with Context Invariant = type!='display'

It appears that this extension is intended to be used on display-type (that is, textual) items, but the context invariant prohibits its use on display-type items. I believe the invariant is incorrect, as SDC calls out using the extension on display-type items.