 
api.NarrativeElement is the parent class of all narrative elements. Those are in particular:
documents.Document: These are generated e.g. by .mmt files and represent the top-level narrative structure of a file. A document is a api.ContainerElement, and as such can contain other elements, namely NarrativeElements. Additionally, each theory in a .mmt file generates a corresponding document that contains all narrative elements of the theory, e.g. documentation comments.documents.NRef is a reference from a document to some other element, specifically
    documents.DRef: A reference to another document (section).documents.MRef: A reference to a module.documents.SRef: A reference to a declaration.opaque.OpaqueElement represents informal elements, such as documentation strings and comments. Most relevant for users are
    opaque.OpaqueXML: represents arbitrary XML andopaque.OpaqueText: represents arbitrary strings. Comments starting with /t in a .mmt file end up as OpaqueTexts.