Clarify the narrative page that if status = extensions, the narrative must reflect the impact of all modifier extensions. Clarify that modifier extensions cannot change the meaning of any elements on Resource or DomainResource (including cannot change the meaning of modifierExtension itself) Note that inclusion of modifier extensions in an instance may limit the ability of other systems to process your instance. Make explicit that implementation guides may place limitations on the appearance of modifier extensions within instances that comply with the implementation guide. Will add some of the examples of modifier processing options from Lloyd's comments below.