the effects of one command. A few exceptional commands are
@dfn{amalgamating}: these commands generally cause small changes to
buffers, so with these a boundary is inserted only every 20th command,
-allowing to undo them as a group. By default, commands
+allowing the changes to be undone as a group. By default, the commands
@code{self-insert-command}, which produces self-inserting input
-characters (@pxref{Commands for Insertion}), and @code{delete-char}
-which deletes characters (@pxref{Deletion}) are amalgamating.
+characters (@pxref{Commands for Insertion}), and @code{delete-char},
+which deletes characters (@pxref{Deletion}), are amalgamating.
Where a command affects the contents of several buffers, as may happen,
for example, when a function on the @code{post-command-hook} affects a
buffer other than the @code{current-buffer}, then @code{undo-boundary}