To index variables.

§1. The index of all the global variables doesn't actually include all of them, because there are "K understood" variables for every kind which can be understood, and a list of those would be tediously repetitive — it would duplicate most of the list of base kinds. So the index shows just one such variable. Inform recognises these variables by parsing their names against the following:

<value-understood-variable-name> ::=
    <k-kind> understood

• This is Preform grammar, not regular C code.

§2. And here is the indexing code:

void IXVariables::index_all(OUTPUT_STREAM) {
    nonlocal_variable *nlv;
    heading *definition_area, *current_area = NULL;
    HTML_OPEN("p");
    Index::anchor(OUT, I"NAMES");
    int understood_note_given = FALSE;
    LOOP_OVER(nlv, nonlocal_variable)
        if ((Wordings::first_wn(nlv->name) >= 0) && (NonlocalVariables::is_global(nlv))) {
            if (<value-understood-variable-name>(nlv->name))
                Index a K understood variable2.1
            else
                Index a regular variable2.2;
        }
    HTML_CLOSE("p");
}

§2.1. Index a K understood variable2.1 =

    if (understood_note_given == FALSE) {
        understood_note_given = TRUE;
        WRITE("<i>kind</i> understood - <i>value</i>");
        HTML_TAG("br");
    }

• This code is used in §2.

§2.2. Index a regular variable2.2 =

    definition_area = Headings::of_wording(nlv->name);
    if (Headings::indexed(definition_area) == FALSE) continue;
    if (definition_area != current_area) {
        wording W = Headings::get_text(definition_area);
        HTML_CLOSE("p");
        HTML_OPEN("p");
        if (Wordings::nonempty(W)) Phrases::Index::index_definition_area(OUT, W, FALSE);
    }
    current_area = definition_area;
    IXVariables::index_one(OUT, nlv);
    HTML_TAG("br");

• This code is used in §2.

§3.

void IXVariables::index_one?Usage of IXVariables::index_one:
§2.2(OUTPUT_STREAM, nonlocal_variable *nlv) {
    WRITE("%+W", nlv->name);
    Index::link(OUT, Wordings::first_wn(nlv->name));
    if (Wordings::nonempty(nlv->var_documentation_symbol)) {
        TEMPORARY_TEXT(ixt)
        WRITE_TO(ixt, "%+W", Wordings::one_word(Wordings::first_wn(nlv->var_documentation_symbol)));
        Index::DocReferences::link(OUT, ixt);
        DISCARD_TEXT(ixt)
    }
    WRITE(" - <i>");
    Kinds::Textual::write(OUT, nlv->nlv_kind);
    WRITE("</i>");
}

void IXVariables::index_stv_set?Usage of IXVariables::index_stv_set:
Actions - §1(OUTPUT_STREAM, shared_variable_set *set) {
    shared_variable *stv;
    LOOP_OVER_LINKED_LIST(stv, shared_variable, set->variables)
        if (stv->underlying_var) {
            HTML::open_indented_p(OUT, 2, "tight");
            IXVariables::index_one(OUT, stv->underlying_var);
            HTML_CLOSE("p");
        }
}