This case-sensitive code system http://hl7.org/fhir/questionnaire-display-category defines the following codes:
Code
Display
Definition
instructions
Instructions
The text provides guidance on how to populate or use a portion of the questionnaire (or the questionnaire as a whole).
security
Security
The text provides guidance on how the information should be or will be handled from a security/confidentiality/access control perspective when completed
help
Help
The text provides additional guidance on populating the containing item. Help text isn't necessarily expected to be rendered as part of the form, but may instead be made available through fly-over, pop-up button, link to a "help" page, etc.