Mention `display-monitor-attributes-list' in docstrings of X11 display measurement functions.

src/ChangeLog

 2013-05-20  YAMAMOTO Mitsuharu  <mituharu@math.s.chiba-u.ac.jp>
 
 	* xfns.c (check_x_display_info): Don't use XINT for terminal object.
+	(Fx_display_pixel_width, Fx_display_pixel_height)
+	(Fx_display_mm_width, Fx_display_mm_height): Mention
+	`display-monitor-attributes-list' in docstrings.
 
 2013-05-18  Paul Eggert  <eggert@cs.ucla.edu>
 

src/xfns.c

@@ -3569,7 +3569,11 @@ DEFUN ("x-display-pixel-width", Fx_display_pixel_width, Sx_display_pixel_width,
        doc: /* Return the width in pixels of the X display TERMINAL.
 The optional argument TERMINAL specifies which display to ask about.
 TERMINAL should be a terminal object, a frame or a display name (a string).
-If omitted or nil, that stands for the selected frame's display.  */)
+If omitted or nil, that stands for the selected frame's display.
+
+On \"multi-monitor\" setups this refers to the pixel width for all
+physical monitors associated with TERMINAL.  To get information for
+each physical monitor, use `display-monitor-attributes-list'.  */)
   (Lisp_Object terminal)
 {
   struct x_display_info *dpyinfo = check_x_display_info (terminal);
@@ -3582,7 +3586,11 @@ DEFUN ("x-display-pixel-height", Fx_display_pixel_height,
        doc: /* Return the height in pixels of the X display TERMINAL.
 The optional argument TERMINAL specifies which display to ask about.
 TERMINAL should be a terminal object, a frame or a display name (a string).
-If omitted or nil, that stands for the selected frame's display.  */)
+If omitted or nil, that stands for the selected frame's display.
+
+On \"multi-monitor\" setups this refers to the pixel height for all
+physical monitors associated with TERMINAL.  To get information for
+each physical monitor, use `display-monitor-attributes-list'.  */)
   (Lisp_Object terminal)
 {
   struct x_display_info *dpyinfo = check_x_display_info (terminal);
@@ -3690,7 +3698,11 @@ DEFUN ("x-display-mm-height", Fx_display_mm_height, Sx_display_mm_height, 0, 1,
        doc: /* Return the height in millimeters of the X display TERMINAL.
 The optional argument TERMINAL specifies which display to ask about.
 TERMINAL should be a terminal object, a frame or a display name (a string).
-If omitted or nil, that stands for the selected frame's display.  */)
+If omitted or nil, that stands for the selected frame's display.
+
+On \"multi-monitor\" setups this refers to the height in millimeters for
+all physical monitors associated with TERMINAL.  To get information
+for each physical monitor, use `display-monitor-attributes-list'.  */)
   (Lisp_Object terminal)
 {
   struct x_display_info *dpyinfo = check_x_display_info (terminal);
@@ -3702,7 +3714,11 @@ DEFUN ("x-display-mm-width", Fx_display_mm_width, Sx_display_mm_width, 0, 1, 0,
        doc: /* Return the width in millimeters of the X display TERMINAL.
 The optional argument TERMINAL specifies which display to ask about.
 TERMINAL should be a terminal object, a frame or a display name (a string).
-If omitted or nil, that stands for the selected frame's display.  */)
+If omitted or nil, that stands for the selected frame's display.
+
+On \"multi-monitor\" setups this refers to the width in millimeters for
+all physical monitors associated with TERMINAL.  To get information
+for each physical monitor, use `display-monitor-attributes-list'.  */)
   (Lisp_Object terminal)
 {
   struct x_display_info *dpyinfo = check_x_display_info (terminal);