diff --git a/lisp/proced.el b/lisp/proced.el
index ebdf61e683c..34566b942b9 100644
--- a/lisp/proced.el
+++ b/lisp/proced.el
@@ -176,7 +176,8 @@ Each element has the form
 
   (KEY NAME FORMAT JUSTIFY PREDICATE REVERSE SORT-SCHEME REFINER).
 
-Symbol KEY is the car of a process attribute.
+Symbol KEY is the symbol of a process attribute, see `process-attributes'
+and `proced-process-attributes'.
 
 String NAME appears in the header line.
 
@@ -279,7 +280,7 @@ The car of each element is a symbol, the name of the format.
 The cdr is a list of attribute keys appearing in `proced-grammar-alist'.
 An element of this list may also be a list of attribute keys that specifies
 alternatives.  If the first attribute is absent for a process, use the second
-one, etc."
+one, etc.  See `process-attributes' for the meaning of each attribute."
   :type '(alist :key-type (symbol :tag "Format Name")
                 :value-type (repeat :tag "Keys"
                                     (choice (symbol :tag "")
@@ -289,7 +290,8 @@ one, etc."
 (defcustom proced-format 'short
   "Current format of Proced listing.
 It can be the car of an element of `proced-format-alist'.
-It can also be a list of keys appearing in `proced-grammar-alist'."
+It can also be a list of keys appearing in `proced-grammar-alist'.
+See `process-attributes' for the meaning of each attribute key."
   :type '(choice (symbol :tag "Format Name")
                  (repeat :tag "Keys" (symbol :tag "")))
   :local t)
@@ -863,7 +865,8 @@ The variable `proced-filter' specifies which system processes are
 displayed.
 
 The variable `proced-format' specifies which attributes are
-displayed for each process.
+displayed for each process.  See `process-attributes' for the
+meaning of each displayed attribute.
 
 Type \\[proced-filter-interactive] and \\[proced-format-interactive] to \
 change the values of `proced-filter' and
@@ -912,7 +915,7 @@ normal hook `proced-post-display-hook'.
 
 ;;;###autoload
 (defun proced (&optional arg)
-  "Generate a listing of UNIX system processes.
+  "Generate a listing of system processes and their attributes.
 \\<proced-mode-map>
 If invoked with optional non-negative ARG, do not select the
 window displaying the process information.
@@ -1898,6 +1901,9 @@ With prefix REVERT non-nil revert listing."
 (defun proced-process-attributes (&optional pid-list)
   "Return alist of attributes for each system process.
 This alist can be customized via `proced-custom-attributes'.
+The function filters the list of attributes returned
+by `process-attributes' by passing each attribute to the
+functions in `proced-custom-attributes'.
 Optional arg PID-LIST is a list of PIDs of system process that are analyzed.
 If no attributes are known for a process (possibly because it already died)
 the process is ignored."