[mediaqueries-4] add example of 'pointer: none' to table, add note about how UA could determine "primary" input (#739)

* Add pointer:none examples, expand stylus examples

- add classic `pointer: none` inputs
- preferred term is digitizers, rather than screens (e.g. Wacom are
external devices, not screens)
- advanced stylus digitizers can sense a hovering stylus, and do trigger
hover interactions - split out basic and advanced stylus
- removed the `<col>` ... appears to serve no actual (styling?) purpose

* Add expansion/clarfication about "primary" input

- adds an introductory paragraph in the main "Interaction Media
Features" section that introduces the concept of primary/all input
mechanisms

- based on the conversation in
#690, add a (non normative)
note hinting at ways in which UAs can potentially determine what is and
isn't primary

* fix linewrapping

Author: patrickhlauke

mediaqueries/Overview.bs

@@ -1571,23 +1571,23 @@ Interaction Media Features</h2>
 		Typical examples of devices matching combinations of 'pointer' and 'hover':
 
 		<table class=data>
-			<col>
-			<col></col>
-			<col></col>
 			<thead>
 				<tr>
 					<td>
+					<th>''pointer: none''
 					<th>''pointer: coarse''
 					<th>''pointer: fine''
 			<tbody>
 				<tr>
 					<th scope=row>''hover: none''
+					<td>keyboard-only controls, sequential/spatial (d-pad) focus navigation
 					<td>smartphones, touch screens
-					<td>stylus-based screens (Cintiq, Wacom, etc)
+					<td>basic stylus digitizers (Cintiq, Wacom, etc)
 				<tr>
 					<th scope=row>''hover: hover''
+					<td>
 					<td>Nintendo Wii controller, Kinect
-					<td>mouse, touch pad
+					<td>mouse, touch pad, advanced stylus digitizers (Surface, Samsung Note, Wacom Intuos Pro, etc)
 		</table>
 		<style>
 			#pointer-hover-table { margin: 1em auto; text-align: center; border-collapse: collapse; max-width: 40em; }
@@ -1597,6 +1597,18 @@ Interaction Media Features</h2>
 		</style>
 	</div>
 
+	The 'pointer' and 'hover' features relate to the characteristics of the “primary” input mechanism, 
+	while 'any-pointer' and 'any-hover' can be used to query the properties of all potentially available input mechanisms.
+
+	Note: While this specification does not define how User Agents should decide what the “primary” input is, 
+	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 input mechanisms available, 
+	and a notion of which of these inputs is generally and/or currently being used. 
+	User Agents may also decide to dynamically change what type of input is deemed to be primary, 
+	in response to changes in the user environment 
+	or in the way the user is interacting with the UA.
+
 <h3 id="pointer">
 Pointing Device Quality: the 'pointer' feature</h3>