Clarify previous undo keys change

Clarify which terminals allow C-/ and which make C-_ easy to type.

diff --git a/doc/emacs/basic.texi b/doc/emacs/basic.texi
index cde7b475d95fce41e5134c804083df7e35378b66..fc856a3acb765a1506ede77e7a846a4d37470546 100644 (file)
--- a/doc/emacs/basic.texi
+++ b/doc/emacs/basic.texi
@@ -464,13 +464,13 @@ Normally, this command undoes the last change, moving point back to
 where it was before the change.  The undo command applies only to
 changes in the buffer; you can't use it to undo cursor motion.
 
-  On a graphics terminal (including text-mode frames displayed by a
-terminal emulator, such as @command{xterm}), the easiest way to invoke
-@code{undo} is with @kbd{C-/}; that doesn't need the Shift key.  On a
-text terminal, @kbd{C-/} does not exist, but in many cases you can type
-@kbd{C-_} without the Shift key (in effect pressing @kbd{C--}) and it
-will work anyway, at least with keyboards that produce the US ASCII
-character set.
+  On a terminal that supports the @key{Control} modifier on all other
+keys, the easiest way to invoke @code{undo} is with @kbd{C-/}, since
+that doesn't need the @key{Shift} modifier.  On terminals which allow
+only the ASCII control characters, @kbd{C-/} does not exist, but many
+of them allow you to omit the @key{Shift} modifier when you type
+@kbd{C-_} (in effect pressing @kbd{C--}), making that the most
+convenient way to invoke @code{undo}.
 
   Although each editing command usually makes a separate entry in the
 undo records, very simple commands may be grouped together.