The "lacuna" style of navigational gadgets, a plain text style with no navigational features at all.

§1. Creation. 

    navigation_design *Lacuna::create(void) {
        navigation_design *ND = Nav::new(I"lacuna", FALSE, TRUE);
        METHOD_ADD(ND, RENDER_CHAPTER_TITLE_MTID, Lacuna::lacuna_chapter_title);
        METHOD_ADD(ND, RENDER_SECTION_TITLE_MTID, Lacuna::lacuna_section_title);
        return ND;
    }

The function Lacuna::create is used in 4/nd (§1).

§2. Top. At the front end of a section, before any of its text. 

    void Lacuna::lacuna_chapter_title(navigation_design *self, text_stream *OUT, volume *V, chapter *C) {
        WRITE("%S\n\n", C->chapter_full_title);
    }

    void Lacuna::lacuna_section_title(navigation_design *self, text_stream *OUT, volume *V, chapter *C, section *S) {
        WRITE("\n%c%S\n\n", SECTION_SYMBOL, S->title);
    }

The function Lacuna::lacuna_chapter_title is used in §1.

The function Lacuna::lacuna_section_title is used in §1.