Open view relative to mouse, take 2

doc/riverctl.1.scd

@@ -300,9 +300,11 @@ matches everything while _\*\*_ and the empty string are invalid.
 	  serial is unknown, the word "Unknown" is used instead.
 	- *position*: Set the initial position of the view, clamping to the bounds
 	  of the output. Requires x and y coordinates of the view as arguments, both
-	  of which must be non-negative. Optionally, the string "mouse" can appear
-	  as the only argument. In this case, the view will appear at the mouse's
-	  position. Applies only to new views.
+	  of which must be non-negative. Applies only to new views.
+    - *relative-position*: Set the position of the view relative to
+      something. Requires the anchor and the x and y coordinates of the
+	  view. The coordinates are either positive or negative numbers that are
+	  relative to the anchor. Applies only to new views.
 	- *dimensions*: Set the initial dimensions of the view, clamping to the
 	  constraints of the view. Requires width and height of the view as
 	  arguments, both of which must be non-negative. Applies only to new views.