Doc updates re completion-in-region-function

* lisp/minibuffer.el (completion-in-region-functions, completion-in-region)
(completion--in-region): Doc fixes.

* doc/lispref/hooks.texi: Update comment.

doc/lispref/hooks.texi

@@ -240,7 +240,6 @@ choose-completion-string-functions
 completing-read-function
 completion-annotate-function
 completion-at-point-functions
-completion-in-region-functions
 completion-list-insert-choice-function
 deactivate-current-input-method-function
 describe-current-input-method-function

lisp/ChangeLog

 2014-05-27  Glenn Morris  <rgm@gnu.org>
+	* minibuffer.el (completion-in-region-functions, completion-in-region)
+	(completion--in-region): Doc fixes.
+
 	* abbrev.el (abbrev-expand-functions, abbrev-expand-function)
 	(expand-abbrev, abbrev--default-expand): Doc fixes.

lisp/minibuffer.el

@@ -1876,14 +1876,14 @@ variables.")
   (exit-minibuffer))
 
 (defvar completion-in-region-functions nil
-  "Wrapper hook around `completion-in-region'.")
+  "Wrapper hook around `completion--in-region'.")
 (make-obsolete-variable 'completion-in-region-functions
                         'completion-in-region-function "24.4")
 
 (defvar completion-in-region-function #'completion--in-region
   "Function to perform the job of `completion-in-region'.
 The function is called with 4 arguments: START END COLLECTION PREDICATE.
-The arguments and expected return value are like the ones of
+The arguments and expected return value are as specified for
 `completion-in-region'.")
 
 (defvar completion-in-region--data nil)
@@ -1901,10 +1901,12 @@ we entered `completion-in-region-mode'.")
 
 (defun completion-in-region (start end collection &optional predicate)
   "Complete the text between START and END using COLLECTION.
-Return nil if there is no valid completion, else t.
 Point needs to be somewhere between START and END.
-PREDICATE (a function called with no arguments) says when to
-exit."
+PREDICATE (a function called with no arguments) says when to exit.
+This calls the function that `completion-in-region-function' specifies
+\(passing the same four arguments that it received) to do the work,
+and returns whatever it does.  The return value should be nil
+if there was no valid completion, else t."
   (cl-assert (<= start (point)) (<= (point) end))
   (funcall completion-in-region-function start end collection predicate))
 
@@ -1916,6 +1918,9 @@ exit."
   :version "22.1")
 
 (defun completion--in-region (start end collection &optional predicate)
+  "Default function to use for `completion-in-region-function'.
+Its arguments and return value are as specified for `completion-in-region'.
+This respects the wrapper hook `completion-in-region-functions'."
   (with-wrapper-hook
       ;; FIXME: Maybe we should use this hook to provide a "display
       ;; completions" operation as well.