; Fix recent improvements in docs of splitting and merging frames

* lisp/window-x.el (merge-frames): Doc fix.

* doc/lispref/windows.texi (Basic Windows): Fix a typo.
* doc/lispref/frames.texi (Splitting and Merging Frames): Fix
wording, markup and indexing.

doc/lispref/frames.texi

@@ -3094,7 +3094,7 @@ criteria.
 @section Splitting and Merging Frames
 @cindex splitting a frame
 @cindex merging two frames
-@cindex Transferring window layouts
+@cindex transferring window layouts to frames
 
 The following two functions are useful to transfer parts of the window
 layout (@pxref{Basic Windows}) of one frame to two separate frames and
@@ -3110,7 +3110,7 @@ Interactively, @var{arg} is the prefix argument.
 In a first step, it divides the child windows (@pxref{Windows and
 Frames}) of @var{frame}'s main window (@pxref{Side Windows}) into two
 parts.  The first part includes the first @var{arg} child windows if
-@var{arg} is positive, and the -@var{arg} last child windows if
+@var{arg} is positive, and the @minus{}@var{arg} last child windows if
 @var{arg} is negative.  The second part includes the remaining child
 windows of @var{frame}'s main window.
 
@@ -3133,20 +3133,22 @@ This command transfers the main window (@pxref{Side Windows}) of
 @var{frame2} to @var{frame1}.  Both @var{frame1} and @var{frame2} must
 specify live frames.
 
-In a first step it splits the main window of @var{frame1}.  If
+In the first step it splits the main window of @var{frame1}.  If
 @var{vertical} is non-@code{nil}, it makes the new window below the old
 main window of @var{frame1}.  Otherwise, it makes the new window on the
 right of @var{frame1}'s main window.
 
-In a second step it makes the new window a clone (@pxref{Window
+In the second step it makes the new window a clone (@pxref{Window
 Configurations}) of the main window of @var{frame2}.  The original
 identity (@pxref{Basic Windows}) of the cloned windows is lost in that
-step.  In a final step, it deletes @var{frame2} if the merge completed
+step.  In the final step, it deletes @var{frame2} if the merge completed
 successfully and returns @var{frame1}.
 
 Interactively, @var{vertical} is the prefix argument, @var{frame1} is
 the selected frame and @var{frame2} is the frame following @var{frame1}
-in the list of all frames (@pxref{Finding All Frames}).
+in the list of all frames (@pxref{Finding All Frames}).  If @var{frame1}
+and @var{frame2} are omitted or @code{nil} in calls from Lisp, they
+default to the above values.
 @end deffn
 
 In general you cannot ``undo'' a @code{split-frame} call with a

doc/lispref/windows.texi

@@ -89,7 +89,7 @@ tiling operations for that frame.
 @cindex window object
 @cindex window identity
 In Emacs Lisp, windows are represented by a special Lisp object type
-(@pxref{Window Type}).  Two windows are identic if and only if they are
+(@pxref{Window Type}).  Two windows are identical if and only if they are
 represented by the same Lisp object.
 
 @defun windowp object

lisp/window-x.el

@@ -319,8 +319,10 @@ ones in `window--transpose'."
 (defun merge-frames (&optional frame1 frame2 vertical)
   "Merge the main window of FRAME2 into FRAME1.
 Split the main window of FRAME1 and make the new window display the main
-window of FRAME2.  Both FRAME1 and FRAME2 must be live frames.  If
-VERTICAL is non-nil, make the new window below the old main window of
+window of FRAME2.  Both FRAME1 and FRAME2 must be live frames.  FRAME1
+defaults to the selected frame and FRAME2 to the frame that follows FRAME1
+in the frame list.
+If VERTICAL is non-nil, make the new window below the old main window of
 FRAME1.  Otherwise, make the new window on the right of FRAME1's main
 window.  Interactively, VERTICAL is the prefix argument, FRAME1 is the
 selected frame and FRAME2 is the frame following FRAME1 in the frame