code: function(start, end, inc) {
      return '(' + start + ' <= ' + end + ') and ' +
          defineUpRange() + '(' + start + ', ' + end + ', ' + inc + ') or ' +
          defineDownRange() + '(' + start + ', ' + end + ', ' + inc + ')';
    }
docs: Arguments are legal Python code (numbers or strings returned by scrub()).