This case-sensitive code system
http://hl7.org/fhir/questionnaire-disabled-display defines the following codes:
Code
Display
Definition
hidden
Hidden
The item (and its children) should not be visible to the user at all.
protected
Protected
The item (and possibly its children) should not be selectable or editable but should still be visible - to allow the user to see what questions
could have been completed had other answers caused the item to be enabled.