How to use the vega-scale.isQuantile function in vega-scale

function singularDomain(domain, spec, scope) {
  var data = scope.getData(domain.data);
  if (!data) dataLookupError(domain.data);

  return isDiscrete(spec.type)
      ? data.valuesRef(scope, domain.field, parseSort(domain.sort, false))
      : isQuantile(spec.type) ? data.domainRef(scope, domain.field)
      : data.extentRef(scope, domain.field);
}

function multipleDomain(domain, spec, scope) {
  var data = domain.data,
      fields = domain.fields.reduce(function(dom, d) {
        d = isString(d) ? {data: data, field: d}
          : (isArray(d) || d.signal) ? fieldRef(d, scope)
          : d;
        dom.push(d);
        return dom;
      }, []);

  return (isDiscrete(spec.type) ? ordinalMultipleDomain
    : isQuantile(spec.type) ? quantileMultipleDomain
    : numericMultipleDomain)(domain, scope, fields);
}