diff --git a/lisp/emacs-lisp/elisp-scope.el b/lisp/emacs-lisp/elisp-scope.el
index 1dad4a558a3..7f66e277b2f 100644
--- a/lisp/emacs-lisp/elisp-scope.el
+++ b/lisp/emacs-lisp/elisp-scope.el
@@ -2828,6 +2828,10 @@ is locally defined, or nil.  If SYM is itself a binding occurrence, then
 POS and DEF are equal.  If SYM is not lexically bound, then DEF is nil
 and so is ID.
 
+CALLBACK should use ID by checking if it is nil or `equal' to other ID
+values produced in the same call to this function.  The specific value
+of a given ID is otherwise meaningless.
+
 As an example, when this function analyzes the following form
 
   (lambda (mode) (let ((mode (or mode major-mode))) (symbol-name mode)))
diff --git a/lisp/progmodes/elisp-mode.el b/lisp/progmodes/elisp-mode.el
index 6ccbe14f265..5a550b33016 100644
--- a/lisp/progmodes/elisp-mode.el
+++ b/lisp/progmodes/elisp-mode.el
@@ -618,7 +618,9 @@ semantic highlighting takes precedence."
 
 If `elisp-add-help-echo' is non-nil, also annotate the symbol with the
 `help-echo' text property.  If `cursor-sensor-mode' is enabled and ID is
-non-nil, also annotate the symbol with `cursor-sensor-functions'.
+non-nil (i.e. SYM is local variable), also annotate the symbol with
+`cursor-sensor-functions' that highlight all occurrences of SYM with the
+same ID whenever point is on this SYM.
 
 For the precise meaning of the arguments of this function, see the
 docstring of `elisp-scope-analyze-form'.  This function is intended for