docs: function concat() {
      var value,
          j = -1,
          length = arguments.length,
          result = slice.call(this),
          index = result.length;
  
      while (++j < length) {
        value = arguments[j];
        if (isClassOf(value, 'Array')) {
          for (var k = 0, l = value.length; k < l; k++, index++) {
            if (k in value) {
              result[index] = value[k];
            }
          }
        } else {
          result[index++] = value;
        }
      }
      return result;
    }