Cover edge-case: primary input not pointer, secondary pointer

Clarifies that it's again up to the UA to decide what to do in these
situations.

Author: patrickhlauke

mediaqueries/Overview.bs

@@ -1604,7 +1604,10 @@ Interaction Media Features</h2>
 	the expectation is that User Agents should make this determination 
 	by combining knowledge about the device/environment they are running on, 
 	the number and type of pointing devices available, 
-	and a notion of which of these is generally and/or currently being used. 
+	and a notion of which of these is generally and/or currently being used.
+	In situations where the primary input mechanism for a device is not a pointing device,
+	but there is a secondary – and less frequently used – input that is a pointing devices,
+	the user agent may decide to treat the non-pointing device as the primary (resulting in 'pointer: none').
 	User Agents may also decide to dynamically change what type of pointing device is deemed to be primary, 
 	in response to changes in the user environment 
 	or in the way the user is interacting with the UA.