diff -ru mutt-1.1.11/doc/manual.sgml mutt-1.1.11-dgc/doc/manual.sgml
--- mutt-1.1.11/doc/manual.sgml	Thu Mar 30 09:23:56 2000
+++ mutt-1.1.11-dgc/doc/manual.sgml	Sun Apr  9 19:17:54 2000
@@ -1604,6 +1604,7 @@
 ~U              unread messages
 ~v		message is part of a collapsed thread.
 ~x EXPR         messages which contain EXPR in the `References' field
+~y EXPR         messages which contain EXPR in the `X-Label' field
 ~z [MIN]-[MAX]  messages with a size in the range MIN to MAX *)
 </verb></tscreen>
 
@@ -1938,6 +1939,16 @@
 ``From'' field.  When unset, the ``Reply-To'' field will be used when
 present.
 
+The ``X-Label:'' header field can be used to further identify mailing
+lists or list subject matter (or just to annotate messages
+individually).  The <ref id="index_format"
+name="&dollar;index&lowbar;format"> variable's ``&percnt;y'' and
+``&percnt;Y'' escapes can be used to expand ``X-Label:'' fields in the
+index, and Mutt's pattern-matcher can match regular expressions to
+``X-Label:'' fields with the ``~y'' selector.  ``X-Label:'' is not a
+standard message header field, but it can easily be inserted by procmail
+and other mail filtering agents.
+
 Lastly, Mutt has the ability to <ref id="sort" name="sort"> the mailbox into
 <ref id="threads" name="threads">.  A thread is a group of messages which all relate to the same
 subject.  This is usually organized into a tree-like structure where a
@@ -3661,6 +3672,12 @@
 %u      user (login) name of the author
 %v      first name of the author, or the 
         recipient if the message is from you
+%y      `x-label:' field, if present
+%Y      `x-label:' field, if present, and
+        (1) not a part of a thread tree;
+        (2) at the top of a thread; or
+        (3) `x-label' is different from
+        preceding message's `x-label'
 %Z      message status flags
 %{fmt}  the date and time of the message is
         converted to sender's time zone, and 
diff -ru mutt-1.1.11/hdrline.c mutt-1.1.11-dgc/hdrline.c
--- mutt-1.1.11/hdrline.c	Fri Mar  3 04:10:08 2000
+++ mutt-1.1.11-dgc/hdrline.c	Sun Apr  9 19:17:54 2000
@@ -216,6 +216,8 @@
  * %T = $to_chars
  * %u = user (login) name of author
  * %v = first name of author, unless from self
+ * %y = `x-label:' field (if present)
+ * %Y = `x-label:' field (if present, tree unfolded, and != parent's x-label)
  * %Z = status flags	*/
 
 struct hdr_format_info
@@ -236,7 +238,7 @@
 		format_flag flags)
 {
   struct hdr_format_info *hfi = (struct hdr_format_info *) data;
-  HEADER *hdr;
+  HEADER *hdr, *htmp;
   CONTEXT *ctx;
   char fmt[SHORT_STRING], buf2[SHORT_STRING], ch, *p;
   int do_locales, i;
@@ -607,6 +609,48 @@
       if ((p = strpbrk (buf2, " %@")))
 	*p = 0;
       snprintf (dest, destlen, fmt, buf2);
+      break;
+
+    case 'y':
+      if (optional)
+      {
+	optional = hdr->env->x_label ? 1 : 0;
+      }
+	snprintf (fmt, sizeof (fmt), "%%%ss", prefix);
+	snprintf (dest, destlen, fmt, NONULL (hdr->env->x_label));
+      break;
+
+    case 'Y':
+      if (hdr->env->x_label)
+      {
+	i = 1;	/* reduce reuse recycle */
+	htmp = NULL;
+	if (flags & M_FORMAT_TREE
+	    && (hdr->prev && hdr->prev->env->x_label))
+	  htmp = hdr->prev;
+	else if (flags & M_FORMAT_TREE
+	    && (hdr->parent && hdr->parent->env->x_label))
+	  htmp = hdr->parent;
+	if (htmp && mutt_strcasecmp (hdr->env->x_label,
+				     htmp->env->x_label) == 0)
+	  i = 0;
+      }
+      else
+	i = 0;
+      if (optional)
+      {
+	optional = i;
+      }
+      if (i)
+      {
+	snprintf (fmt, sizeof (fmt), "%%%ss", prefix);
+	snprintf (dest, destlen, fmt, NONULL (hdr->env->x_label));
+      }
+      else
+      {
+	snprintf (fmt, sizeof (fmt), "%%%ss", prefix);
+	snprintf (dest, destlen, fmt, "");
+      }
       break;
 
     case 'Z':
diff -ru mutt-1.1.11/mutt.h mutt-1.1.11-dgc/mutt.h
--- mutt-1.1.11/mutt.h	Wed Mar 22 02:18:55 2000
+++ mutt-1.1.11-dgc/mutt.h	Sun Apr  9 19:17:54 2000
@@ -199,6 +199,7 @@
   M_PGP_ENCRYPT,
   M_PGP_KEY,
 #endif
+  M_XLABEL,
   
   /* Options for Mailcap lookup */
   M_EDIT,
@@ -459,6 +460,7 @@
   char *message_id;
   char *supersedes;
   char *date;
+  char *x_label;
   LIST *references;		/* message references (in reverse order) */
   LIST *userhdrs;		/* user defined headers */
 } ENVELOPE;
diff -ru mutt-1.1.11/parse.c mutt-1.1.11-dgc/parse.c
--- mutt-1.1.11/parse.c	Tue Mar  7 18:06:47 2000
+++ mutt-1.1.11-dgc/parse.c	Sun Apr  9 19:17:54 2000
@@ -1185,6 +1185,11 @@
 	  }
 	  matched = 1;
 	}
+	else if (mutt_strcasecmp (line+1, "-label") == 0)
+	{
+	  e->x_label = safe_strdup(p);
+	  matched = 1;
+	}
 	    
       default:
 	break;
diff -ru mutt-1.1.11/pattern.c mutt-1.1.11-dgc/pattern.c
--- mutt-1.1.11/pattern.c	Fri Mar  3 04:10:11 2000
+++ mutt-1.1.11-dgc/pattern.c	Sun Apr  9 19:17:54 2000
@@ -88,6 +88,7 @@
   { 'U', M_UNREAD,		0,		NULL },
   { 'v', M_COLLAPSED,		0,		NULL },
   { 'x', M_REFERENCE,		0,		eat_regexp },
+  { 'y', M_XLABEL,		0,		eat_regexp },
   { 'z', M_SIZE,		0,		eat_range },
   { 0 }
 };
@@ -890,6 +891,8 @@
    case M_PGP_KEY:
      return (pat->not ^ (h->pgp & PGPKEY));
 #endif
+    case M_XLABEL:
+      return (pat->not ^ (h->env->x_label && regexec (pat->rx, h->env->x_label, 0, NULL, 0) == 0));
   }
   mutt_error (_("error: unknown op %d (report this error)."), pat->op);
   return (-1);