docs: function(separator, group_length, suffix) {
          separator = separator || ' ';
          group_length = group_length || 3;
          suffix = suffix || '';
  
          return function(now, tween) {
            var negative = now < 0,
                floored_number = Math.floor((negative ? -1 : 1) * now),
                separated_number = floored_number.toString(),
                target = $(tween.elem);
  
            if (separated_number.length > group_length) {
              var number_parts = extract_number_parts(separated_number, group_length);
  
              separated_number = remove_precending_zeros(number_parts).join(separator);
              separated_number = reverse(separated_number);
            }
  
            target.prop('number', now).text((negative ? '-' : '') + separated_number + suffix);
          };
        }