Improve documentation and UI of 'C-x v L'

* lisp/vc/vc.el (vc-print-root-log): Improve the wording of
the doc string and of the prompt for the root directory.

* etc/NEWS: Improve and expand the wording of the changes in
'C-x v L'.

* doc/emacs/maintaining.texi (VC Change Log): Improve and
clarify wording of the 'C-x v L' description.

1 files changed, 8 insertions, 2 deletions

diff --git a/doc/emacs/maintaining.texi b/doc/emacs/maintaining.texi
index c1f7aed114f..66fa54113f9 100644
--- a/doc/emacs/maintaining.texi
+++ b/doc/emacs/maintaining.texi
@@ -993,8 +993,14 @@ version-controlled directory tree (RCS, SCCS, CVS, and SRC do not
 support this feature).  With a prefix argument, the command prompts
 for the maximum number of revisions to display.  A numeric prefix
 argument specifies the maximum number of revisions without prompting.
-When the numeric prefix argument is @kbd{M-1}, the command prompts
-for the revision ID, and displays its log entry with a diff of changes.
+When the numeric prefix argument is 1, as in @w{@kbd{C-1 C-x v L}} or
+@w{@kbd{C-u 1 C-x v L}}, the command prompts for the revision ID, and
+displays the log entry of that revision together with the changes
+(diffs) it introduced.  (Some less capable version control systems,
+such as RCS and CVS, don't have commands to show a revision log with
+its diffs; for them the command displays only the log entry, and you
+can request to show the diffs by typing @kbd{d} or @kbd{D}, see
+below.)
 
   The @kbd{C-x v L} history is shown in a compact form, usually
 showing only the first line of each log entry.  However, you can type