Index: src/buffer.h
===================================================================
RCS file: /cvsroot/emacs/emacs/src/buffer.h,v
retrieving revision 1.85
diff -u -d -r1.85 buffer.h
--- src/buffer.h	10 Jan 2002 11:13:17 -0000	1.85
+++ src/buffer.h	15 Jun 2002 17:38:29 -0000
@@ -594,10 +594,11 @@
   Lisp_Object category_table;
 
   /* Values of several buffer-local variables.  */
-  /* tab-width is buffer-local so that redisplay can find it
-     in buffers that are not current.  */
+  /* tab-width and display-tab-width are buffer-local so that
+     redisplay can find it in buffers that are not current.  */
   Lisp_Object case_fold_search;
   Lisp_Object tab_width;
+  Lisp_Object display_tab_width;
   Lisp_Object fill_column;
   Lisp_Object left_margin;
   /* Function to call when insert space past fill column.  */
Index: src/buffer.c
===================================================================
RCS file: /cvsroot/emacs/emacs/src/buffer.c,v
retrieving revision 1.388
diff -u -d -r1.388 buffer.c
--- src/buffer.c	8 Jun 2002 20:25:31 -0000	1.388
+++ src/buffer.c	15 Jun 2002 17:38:30 -0000
@@ -4859,6 +4859,7 @@
   XSETFASTINT (buffer_defaults.overlay_center, BEG);
 
   XSETFASTINT (buffer_defaults.tab_width, 8);
+  buffer_defaults.display_tab_width = Qnil;
   buffer_defaults.truncate_lines = Qnil;
   buffer_defaults.ctl_arrow = Qt;
   buffer_defaults.direction_reversed = Qnil;
@@ -4919,6 +4920,7 @@
   XSETFASTINT (buffer_local_flags.selective_display_ellipses, idx); ++idx;
 #endif
   XSETFASTINT (buffer_local_flags.tab_width, idx); ++idx;
+  XSETFASTINT (buffer_local_flags.display_tab_width, idx); ++idx;
   XSETFASTINT (buffer_local_flags.truncate_lines, idx); ++idx;
   XSETFASTINT (buffer_local_flags.ctl_arrow, idx); ++idx;
   XSETFASTINT (buffer_local_flags.fill_column, idx); ++idx;
@@ -5288,7 +5290,28 @@
 
   DEFVAR_PER_BUFFER ("tab-width", &current_buffer->tab_width,
 		     make_number (Lisp_Int),
-		     doc: /* *Distance between tab stops (for display of tab characters), in columns.  */);
+		     doc: /* *Distance between tab stops, in columns.
+Historically, this variable was only meant to represent the number of
+columns which compose a tab character for display purposes.  However,
+a number of packages began to use it for conversion between tab and
+space characters (e.g. `tabify'), as well as calculating how many
+tab/space characters to insert into a buffer (e.g. CC mode).
+
+Therefore, the variable `display-tab-width' (which see) was introduced
+to allow you to control the display of a tab character, independently
+of how many columns (space characters) you wish it to actually occupy
+in the buffer.  */);
+
+  DEFVAR_PER_BUFFER ("display-tab-width", &current_buffer->display_tab_width,
+		     make_number (Lisp_Int),
+		     doc: /* *Distance between tab stops (for display of tab characters), in columns.
+In addition to an integer, this variable can also be nil, in which
+case the value of `tab-width' is used.
+
+This variable is only meant for controlling how literal tab characters
+are displayed to the user; do not use it to convert between tab and
+actual space characters or other purposes!  Instead, use the variable
+`tab-width' for that. */);
 
   DEFVAR_PER_BUFFER ("ctl-arrow", &current_buffer->ctl_arrow, Qnil,
 		     doc: /* *Non-nil means display control chars with uparrow.