Fixed Arnaud's comments, add support for mocking sources

Author: kenchris

index.html

@@ -161,6 +161,10 @@ <h3>Supported sources</h3>
       <em>global system thermals</em> and the <em>central [=processing unit=]</em>, also know as the CPU.
       Future levels of this specification MAY introduce additional [=source types=].
     </p>
+    <p>
+      If a [=virtual pressure source=] exists, the [=supported source types=] is equal to the
+      [=source types=] [=map/keys=] in the [=virtual pressure source mapping=] [=ordered map=].
+    </p>
     <pre class="idl">
       enum PressureSource { "thermals", "cpu" };
     </pre>
@@ -1609,7 +1613,7 @@ <h2>
     Automation
   </h2>
   <p>
-    The Compute Pressure API pose a challenge to test authors, as fully
+    The Compute Pressure API poses a challenge to test authors, as fully
     exercising interface requires physical hardware devices that respond in predictable ways.
 
     To address this challenge this document defines a [[WEBDRIVER2]] [=extension
@@ -1671,7 +1675,7 @@ <h4>
     </tr>
   </table>
   <p>
-    This [=extension command=] creates a new [=virtual pressure source=] of a certain
+    This [=extension command=] creates a new [=virtual pressure source=] of a specified
     [=source type=]. Calls to {{PressureObserver/observe()}} from {{PressureObserver}} instances
     of the same [=source type=] will cause this [=virtual pressure source=] to be used as their
     backing pressure source until [[[#delete-virtual-pressure-source]]] is run.
@@ -1809,6 +1813,13 @@ <h4>
     additional [=pending state updates=] and turning on and off reporting by setting the
     [=sample update interval=].
   </p>
+  <aside class="note" data-cite="WEBDRIVER2">
+    Additionally, the [=extension command=] can be used to check whether a source type is created
+    via the [[[#create-virtual-pressure-source]]] [=extension command=] by checking the response.
+    If it has not been created the response will contain the [=error=] with
+    [=error code|WebDriver error code=]
+    <a data-cite="webdriver2/#dfn-unsupported-operation">unsupported operation</a>.
+  </aside>
   <table class="data">
     <caption>
       Properties of the parameters argument used by this algorithm
@@ -1866,7 +1877,8 @@ <h4>
     </li>
     <li>
       If |topLevelVirtualPressureSourceMapping| does not [=map/contain=] |virtualPressureSource|,
-      return [=error=] with [=error code|WebDriver error code=] [=invalid argument=].
+      return [=error=] with [=error code|WebDriver error code=]
+      <a data-cite="webdriver2/#dfn-unsupported-operation">unsupported operation</a>.
     </li>
     <li>
       Let |virtualPressureSource| be |topLevelVirtualPressureSourceMapping|[|virtualPressureSourceType|].
@@ -1904,10 +1916,10 @@ <h4>
           If |sampleInterval| is not an Number, return [=error=] with [=error code|WebDriver error code=] [=invalid argument=].
         </li>
         <li>
-          If |sampleInterval| is negative, stop updating the [=mock platform collector=].
+          If |sampleInterval| is &lt; 0, stop updating the [=mock platform collector=].
         </li>
         <li>
-          If |sampleInterval| is positive, start updating the [=mock platform collector=] each |sampleInterval| milliseconds:
+          If |sampleInterval| is &ge; 0, start updating the [=mock platform collector=] each |sampleInterval| milliseconds:
           <ol>
             <li>
               Let |state| be the result of [=stack/pop|popping=] a value from [=pending state updates=].