function reserve(name, func) {
    var x = type(name, func);
    x.identifier = true;
    x.reserved = true;
    return x;
  }
Convenience function for defining JSHint symbols for reserved
keywords--those that are restricted from use as bindings (and as property
names in ECMAScript 3 environments).

@param {string} s - the name of the symbol
@param {function} func - the first null denotation function for the
                         symbol; see the `expression` function for more
                         detail

@returns {object} - the object describing the JSHint symbol (provided to
                    support cases where further refinement is necessary)