code: function bundle (str, header) {
      return _.extend(header, {
        valueOf:  function () { return str; },
        toString: function () { return str; }
      });
    }
docs: /*
  This function takes advantage of JavaScript feature for objects
  that whenever an object is conctenated to a string, the
  toString() method is invoked.
  
  valueOf() is useful in comparisons.