JavaScript API – what is the value bound to '$' in the global namespace?

If we evaluate Object.keys(this) in the Drafts 5 JSContext, we get a recognisable list of the top-level names in the documented Drafts 5 API.

The only name that I don’t immediately recognise, or see in the documentation, is $.

Is $ private API, or is it bound to something that might be helpful to a user ?


(To see a fuller listing of the API, you can create a Script Action containing:

(function() {

    const main = () => {

        const
            g = this,
            ks = keySort(
                Object.keys(g)
            );

        // NEW DRAFTS 5 SHEET
        editor.new();

        // POPULATED WITH LISTING OF OBJECTS PROPERTIES AND METHODS
        // IN THE DRAFTS 5 JAVASCRIPT INTERFACE
        editor.setText(
            ks.map(k => {
                const
                    o = g[k],
                    c = o.constructor,
                    t = typeof c,
                    blnC = t !== 'object',
                    noise = ['constructor', 'prototype'],

                    nest = Object.getOwnPropertyNames(
                        blnC ? (
                            o
                        ) : o.constructor.prototype
                    ).filter(x => !noise.includes(x)),

                    rest = blnC ? Object.getOwnPropertyNames(
                        o.prototype
                    ).filter(x => !noise.includes(x)) : [],

                    fs = nest.concat(rest);

                return k + '\n' + (fs.length > 0 ? (
                    keySort(fs).map(s => '    ' + s).join('\n')
                ) : '');
            }).join('\n')
        );
    };

    const keySort = xs => {
        const ys = xs.slice(0);
        return (
            ys.sort((a, b) => {
                const
                    la = a.toLowerCase(),
                    lb = b.toLowerCase();
                return la < lb ? -1 : la > lb ? 1 : 0;
            }),
            ys
        );
    };

    const showJSON = x => JSON.stringify(x, null, 2);

    // -------------------------------
    return main();
})();

PS I see it’s bound to an instance of ActionKit.ScriptEngine, not sure if that has any user-usable methods ?