Document the user-level features of the Xref package

* doc/emacs/maintaining.texi (Maintaining): Add a list of
described features.
(Xref): New section, made out of thoroughly rewritten "Tags"
section.
(Find Identifiers, Looking Up Identifiers, Xref Commands)
(Identifier Search, List Identifiers): New subsections,
incorporating the old tags commands and the new xref commands.
(Tags Tables, Tag Syntax, Create Tags Table, Etags Regexps):
Section and subsections demoted to a lower level.
* doc/emacs/search.texi (Search):
* doc/emacs/windows.texi (Pop Up Window):
* doc/emacs/frames.texi (Creating Frames):
* doc/emacs/programs.texi (Imenu, Symbol Completion):
* doc/emacs/building.texi (Grep Searching):
* doc/emacs/dired.texi (Operating on Files):
* doc/emacs/glossary.texi (Glossary): All references to tags changed.

1 files changed, 3 insertions, 2 deletions

diff --git a/doc/emacs/windows.texi b/doc/emacs/windows.texi
index cd7d08dede6..f99234b5c1b 100644
--- a/doc/emacs/windows.texi
+++ b/doc/emacs/windows.texi
@@ -231,8 +231,9 @@ Mail}), but in another window (@code{compose-mail-other-window}).
 
 @findex find-tag-other-window
 @item C-x 4 .
-Find a tag in the current tags table, similar to @kbd{M-.}
-(@pxref{Tags}), but in another window (@code{find-tag-other-window}).
+Find the definition of an identifier, similar to @kbd{M-.}
+(@pxref{Xref}), but in another window
+(@code{xref-find-definitions-other-window}).
 @item C-x 4 r @var{filename} @key{RET}
 Visit file @var{filename} read-only, and select its buffer in another
 window (@code{find-file-read-only-other-window}).  @xref{Visiting}.