Improve Emacs user manual in fixit.texi

* doc/emacs/fixit.texi (Undo): Clarify inaccurate description of
repeated undo.
(Transpose): Describe explicitly what happens at EOL.
(Spelling): Use "spell-checking" consistently.  Clarify wording.
Suggested by Toon Claes <toon@iotcl.com> in
emacs-manual-bugs@gnu.org.

doc/emacs/fixit.texi

@@ -69,10 +69,10 @@ changes have already been undone, the undo command signals an error.
   Any command other than an undo command breaks the sequence of undo
 commands.  Starting from that moment, the entire sequence of undo
 commands that you have just performed are themselves placed into the
-undo record, as a single set of changes.  Therefore, to re-apply
-changes you have undone, type @kbd{C-f} or any other command that
-harmlessly breaks the sequence of undoing; then type @kbd{C-/} to undo
-the undo command.
+undo record.  Therefore, to re-apply changes you have undone, type
+@kbd{C-f} or any other command that harmlessly breaks the sequence of
+undoing; then type @kbd{C-/} one or more times to undo some of the
+undo commands.
 
   Alternatively, if you want to resume undoing, without redoing
 previous undo commands, use @kbd{M-x undo-only}.  This is like
@@ -180,7 +180,8 @@ Otherwise, a reverse search (@kbd{C-r}) is often the best way.
 dragging the word preceding or containing point forward as well.  The
 punctuation characters between the words do not move.  For example,
 @w{@samp{FOO, BAR}} transposes into @w{@samp{BAR, FOO}} rather than
-@samp{@w{BAR FOO,}}.
+@samp{@w{BAR FOO,}}.  When point is at the end of the line, it will
+transpose the word before point with the first word on the next line.
 
   @kbd{C-M-t} (@code{transpose-sexps}) is a similar command for
 transposing two expressions (@pxref{Expressions}), and @kbd{C-x C-t}
@@ -344,16 +345,16 @@ wildcard.
 
 @item C-g
 @itemx X
-Quit interactive spell checking, leaving point at the word that was
+Quit interactive spell-checking, leaving point at the word that was
 being checked.  You can restart checking again afterward with @kbd{C-u
 M-$}.
 
 @item x
-Quit interactive spell checking and move point back to where it was
-when you started spell checking.
+Quit interactive spell-checking and move point back to where it was
+when you started spell-checking.
 
 @item q
-Quit interactive spell checking and kill the spell-checker subprocess.
+Quit interactive spell-checking and kill the spell-checker subprocess.
 
 @item ?
 Show the list of options.
@@ -371,7 +372,7 @@ character; type that digit or character to choose it.
 @cindex @code{ispell} program
 @findex ispell-kill-ispell
   Once started, the spell-checker subprocess continues
-to run, waiting for something to do, so that subsequent spell checking
+to run, waiting for something to do, so that subsequent spell-checking
 commands complete more quickly.  If you want to get rid of the
 process, use @kbd{M-x ispell-kill-ispell}.  This is not usually
 necessary, since the process uses no processor time except when you do
@@ -392,19 +393,21 @@ so that it will use a different standard dictionary.  Your personal
 dictionary is specified by the variable
 @code{ispell-personal-dictionary}.  If that is @code{nil}, the
 spelling program looks for a personal dictionary in a default
-location.
+location, which is specific to each spell-checker.
 
 @vindex ispell-complete-word-dict
   A separate dictionary is used for word completion.  The variable
 @code{ispell-complete-word-dict} specifies the file name of this
 dictionary.  The completion dictionary must be different because it
-cannot use root and affix information.  For some languages, there
-is a spell checking dictionary but no word completion dictionary.
+cannot use the information about roots and affixes of the words, which
+spell-checking uses to detect variations of words.  For some
+languages, there is a spell-checking dictionary but no word completion
+dictionary.
 
 @cindex Flyspell mode
 @cindex mode, Flyspell
 @findex flyspell-mode
-  Flyspell mode is a minor mode that performs automatic spell checking
+  Flyspell mode is a minor mode that performs automatic spell-checking
 as you type.  When it finds a word that it does not recognize, it
 highlights that word.  Type @kbd{M-x flyspell-mode} to toggle Flyspell
 mode in the current buffer.  To enable Flyspell mode in all text mode