Modified the new agenda tag filtering command.

ORGWEBPAGE/Changes.org

@@ -38,17 +38,22 @@
     agenda view with respect to a tag.  This command is executed
     with the =/= key in the agenda.  You will be prompted for a
     tag selection key, and all entries that do not contain or
-    inherit the corresponding tag will be removed from the agenda
-    view.  With a prefix argument, the complementary filter is
-    applied: entries that do have the tag will be removed.
-    Narrowing the search results down with several successive
-    filtering operations is possible.
+    inherit the corresponding tag will be hidden.  With a prefix
+    argument, the complementary filter is applied: entries that
+    do have the tag will be hidden.
 
-    Note that this only removes the entries from the agenda
-    buffer, but it does not modify the query.  Therefore, the =r=
-    and =g= keys will restore the original agenda buffer.
+    This operation only hides lines in the agenda buffer.  It
+    does not initiate a new search and therefore is very fast.
 
-    This functionality was John Wiegleys idea and is a simpler
+    If you press TAB at the tag selection prompt, you will be
+    switched to a completion interface to select a tag.  This is
+    useful in particular when you want to select a tag that does
+    not have a direct access character.
+
+    A double =/ /= will restore the original agenda view by
+    unhiding any hidden lines.
+
+    This functionality was John Wiegley's idea.  It is a simpler
     implementation of some of the query-editing features proposed
     and implemented some time ago by Christopher League (see the
     file contrib/lisp/org-interactive-query.el).

ORGWEBPAGE/index.org

@@ -102,7 +102,7 @@ Some more information about this can be found in the [[http://orgmode.org/worg/o
 ** Reference card
    - Download the [[file:orgcard.pdf][Refcard]] for org-mode
    - Kyle Sherman has created a [[file:orgcard.txt][text version]] of the reference card
-     (Org version 6.06).
+     (Org version 6.07).
 ** The FAQ
    - The [[http://orgmode.org/worg/org-faq.php][Org Mode FAQ]] is user-editable and is maintained by the [[http://orgmode.org/worg/][Worg
      project]]. 

doc/org.texi

@@ -5806,9 +5806,12 @@ that entry would be in the original buffer (taken from a property, from a
 @kindex /
 @item /
 Filter the current agenda view with respect to a tag.  You will be prompted
-for a tag selection letter and all entries that do not contain this tag will
-be removed from the agenda display.  When called with prefix arg, remove the
-entries that @emph{do} have the tag.
+for a tag selection letter.  Pressing @key{TAB} at that prompt will offer use
+completion to select a tag (including any tags that do not have a selection
+character).  The command then hides all entries that do not contain or
+inherit this tag.  When called with prefix arg, remove the entries that
+@emph{do} have the tag.  A second @kbd{/} at the prompt will unhide any
+hidden entries.
 
 @kindex [
 @kindex ]

doc/orgcard.tex

@@ -612,7 +612,7 @@ after  ``{\tt :}'', and dictionary words elsewhere.
 \key{find stuck projects}{C-c a \#$^1$}
 \key{show timeline of current org file}{C-c a L$^1$}
 \key{configure custom commands}{C-c a C$^1$}
-\key{configure stuck projects}{C-c a !$^1$}
+%\key{configure stuck projects}{C-c a !$^1$}
 \key{agenda for date at cursor}{C-c C-o}
 
 {\bf Commands available in an agenda buffer}
@@ -637,6 +637,7 @@ after  ``{\tt :}'', and dictionary words elsewhere.
 \key{toggle display of logbook entries}{l}
 \key{toggle inclusion of archived trees/files}{v / C-u v}
 \key{refresh agenda buffer with any changes}{r / g}
+\key{filter with repect to a tag}{/}
 \key{save all org-mode buffers}{s}
 \key{display next/previous day,week,...}{RIGHT/LEFT}
 \key{goto today}{.}

doc/orgcard.txt

@@ -1,5 +1,5 @@
 ================================================================================
-Org-Mode Reference Card (for version 6.06)
+Org-Mode Reference Card (for version 6.07)
 ================================================================================
 
 ================================================================================
@@ -358,6 +358,7 @@ toggle time grid for daily schedule               G
 toggle display of logbook entries                 l
 toggle inclusion of archived trees/files          v / C-u v}
 refresh agenda buffer with any changes            r / g
+filter agenda with repect to a tag                /
 save all org-mode buffers                         s
 display the next/previous day, week,...           RIGHT/LEFT
 goto today                                        .

lisp/org-agenda.el

@@ -4085,25 +4085,49 @@ The tag is selected with its fast selection letter, as configured.
 With prefix argument STRIP, remove all lines that do have the tag."
   (interactive "P")
   (let (char a tag (inhibit-read-only t))
-    (message "Tag selection character [%s]"
-	     (mapconcat
-	      (lambda (x) (if (cdr x) (char-to-string (cdr x)) ""))
-	      org-tag-alist-for-agenda ""))
-    (setq char (read-char-exclusive))
-    (unless (setq a (rassoc char org-tag-alist-for-agenda))
-      (error "invalid tag selection character %c" char))
-    (setq tag (car a))
-    (save-excursion
-      (goto-char (point-min))
-      (while (not (eobp))
-	(if (get-text-property (point) 'org-marker)
-	    (progn
-	      (setq tags (get-text-property (point) 'tags))
-	      (if (or (and (member tag tags) strip)
-		      (and (not (member tag tags)) (not strip)))
-		  (delete-region (point) (1+ (point-at-eol)))
-		(beginning-of-line 2)))
-	  (beginning-of-line 2))))))
+      (message "Select tag [%s], [TAB] to complete, [/] to restore: "
+	       (mapconcat
+		(lambda (x) (if (cdr x) (char-to-string (cdr x)) ""))
+		org-tag-alist-for-agenda ""))
+      (setq char (read-char))
+      (when (equal char ?\t)
+	(unless (local-variable-p 'org-global-tags-completion-table)
+	  (org-set-local 'org-global-tags-completion-table
+			 (org-global-tags-completion-table)))
+	(let ((completion-ignore-case t))
+	  (setq tag (completing-read
+		     "Tag: " org-global-tags-completion-table))))
+      (cond
+       ((equal char ?/) (org-agenda-filter-by-tag-show-all))
+       ((or (setq a (rassoc char org-tag-alist-for-agenda))
+	    (and tag (setq a (cons tag nil))))
+	(org-agenda-filter-by-tag-show-all)
+	(setq tag (car a))
+	(save-excursion
+	  (goto-char (point-min))
+	  (while (not (eobp))
+	    (if (get-text-property (point) 'org-marker)
+		(progn
+		  (setq tags (get-text-property (point) 'tags))
+		  (if (or (and (member tag tags) strip)
+			  (and (not (member tag tags)) (not strip)))
+		      (org-agenda-filter-by-tag-hide-line))
+		  (beginning-of-line 2))
+	      (beginning-of-line 2)))))
+       (t (error "Invalid tag selection character %c" char)))))
+
+(defvar org-agenda-filter-overlays nil)
+
+(defun org-agenda-filter-by-tag-hide-line ()
+  (let (ov)
+    (setq ov (org-make-overlay (point-at-bol) (1+ (point-at-eol))))
+    (org-overlay-put ov 'invisible t)
+    (org-overlay-put ov 'type 'tags-filter)
+    (push ov org-agenda-filter-overlays)))
+
+(defun org-agenda-filter-by-tag-show-all ()
+  (mapc 'org-delete-overlay org-agenda-filter-overlays)
+  (setq org-agenda-filter-overlays nil))
 
 (defun org-agenda-manipulate-query-add ()
   "Manipulate the query by adding a search term with positive selection.