To write the Values element (Vl) in the index.

§1. Variables and equations both appear here, though really they're conceptually quite different. 

void ValuesElement::render(OUTPUT_STREAM, index_session *session) {
    localisation_dictionary *LD = Indexing::get_localisation(session);
    tree_inventory *inv = Indexing::get_inventory(session);
    InterNodeList::array_sort(inv->variable_nodes, MakeSynopticModuleStage::module_order);
    Index the variables1.1;
    InterNodeList::array_sort(inv->equation_nodes, MakeSynopticModuleStage::module_order);
    Index the equations1.2;
}

§1.1. Index the variables1.1 = 

    inter_symbol *definition_area = NULL, *current_area = NULL;
    HTML_OPEN("p");
    IndexUtilities::anchor(OUT, I"NAMES");
    int understood_note_given = FALSE;
    inter_package *pack;
    LOOP_OVER_INVENTORY_PACKAGES(pack, i, inv->variable_nodes)
        if (Metadata::read_optional_numeric(pack, I"^indexable")) {
            if (Metadata::read_optional_numeric(pack, I"^understood"))
                Index a K understood variable1.1.1
            else
                Index a regular variable1.1.2;
        }
    HTML_CLOSE("p");

§1.1.1. Index a K understood variable1.1.1 = 

    if (understood_note_given == FALSE) {
        understood_note_given = TRUE;
        Localisation::roman(OUT, LD, I"Index.Elements.Vl.UnderstoodVariables");
        HTML_TAG("br");
    }

§1.1.2. Index a regular variable1.1.2 = 

    definition_area = Metadata::optional_symbol(pack, I"^heading");
    if (definition_area == NULL) continue;
    if (definition_area != current_area) {
        inter_package *heading_pack =
            InterPackage::container(definition_area->definition);
        HTML_CLOSE("p");
        HTML_OPEN("p");
        IndexUtilities::show_definition_area(OUT, heading_pack, FALSE);
    }
    current_area = definition_area;

    text_stream *name = Metadata::optional_textual(pack, I"^name");
    WRITE("%S", name);
    IndexUtilities::link_package(OUT, pack);
    IndexUtilities::link_to_documentation(OUT, pack);
    text_stream *contents = Metadata::optional_textual(pack, I"^contents");
    WRITE(" - <i>%S</i>", contents);
    HTML_TAG("br");

§1.2. Index the equations1.2 = 

    HTML_OPEN("p");
    Localisation::bold(OUT, LD, I"Index.Elements.Vl.EquationsHeading");
    WRITE(" (");
    Localisation::italic(OUT, LD, I"Index.Elements.Vl.AboutEquations");
    WRITE(")");
    HTML_CLOSE("p");
    HTML_OPEN("p");
    int N = 0;
    inter_package *pack;
    LOOP_OVER_INVENTORY_PACKAGES(pack, i, inv->equation_nodes) {
        int at = (int) Metadata::read_optional_numeric(pack, I"^at");
        if (at > 0) {
            WRITE("%S", Metadata::optional_textual(pack, I"^name"));
            IndexUtilities::link(OUT, at);
            WRITE(" (%S)", Metadata::optional_textual(pack, I"^text"));
            HTML_TAG("br");
            N++;
        }
    }
    if (N == 0) Localisation::italic(OUT, LD, I"Index.Elements.Vl.NoEquations");
    HTML_CLOSE("p");