src/dispextern.h: Fix commentary to it's hpos member.

diff --git a/src/dispextern.h b/src/dispextern.h
index 8ccc3d35d8c306ec87896ff98c48ea02186c16a7..6027d5ee7ed89affb564f3ce14c42693af0b8b41 100644 (file)
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -2599,7 +2599,8 @@ struct it
   int vpos;
 
   /* Horizontal matrix position reached in move_it_in_display_line.
-     Only set there, not in display_line.  */
+     Only set there, not in display_line, and only when the X
+     coordinate is past first_visible_x.  */
   int hpos;
 
   /* Left fringe bitmap number (enum fringe_bitmap_type).  */