```common lisp
;;;; -*- Mode: LISP; Syntax: COMMON-LISP; Package: CL-USER; Base: 10 -*-

;;;;     Copyright (C) 2014  Varoun. P

;;;;     This program is free software: you can redistribute it and/or modify
;;;;     it under the terms of the GNU Affero General Public License as
;;;;     published by the Free Software Foundation, either version 3 of the
;;;;     License, or (at your option) any later version.

;;;;     This program is distributed in the hope that it will be useful,
;;;;     but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;;     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;;;     GNU Affero General Public License for more details.

;;;;     You should have received a copy of the GNU Affero General Public License
;;;;     along with this program.  If not, see <http://www.gnu.org/licenses/>.


(in-package "STREAMLETS-IMPL")

;;;; The foundation class for all tuples.

(defclass tuple ()
  ((metrics 
    :initarg :tuple-metrics 
    :initform nil 
    :accessor tuple-metrics
    :documentation "A list of metrics relevant to tuple processing.")))

```

Add documentation to the tuple class.
user
```common lisp
;;;; -*- Mode: LISP; Syntax: COMMON-LISP; Package: CL-USER; Base: 10 -*-

;;;;     Copyright (C) 2014  Varoun. P

;;;;     This program is free software: you can redistribute it and/or modify
;;;;     it under the terms of the GNU Affero General Public License as
;;;;     published by the Free Software Foundation, either version 3 of the
;;;;     License, or (at your option) any later version.

;;;;     This program is distributed in the hope that it will be useful,
;;;;     but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;;     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;;;     GNU Affero General Public License for more details.

;;;;     You should have received a copy of the GNU Affero General Public License
;;;;     along with this program.  If not, see <http://www.gnu.org/licenses/>.


(in-package "STREAMLETS-IMPL")

;;;; Streamlets Tuples

(defclass tuple ()
  ((metrics 
    :initarg :tuple-metrics 
    :initform nil 
    :accessor tuple-metrics
    :documentation "A list of metrics relevant to tuple processing."))
  (:documentation "The foundation for all tuples."))
```
assistant