Address feedback from nell

toji · toji · commit 158ff4a1fea6 · 2019-02-06T22:43:57.000Z
diff --git a/index.bs b/index.bs
@@ -3,7 +3,10 @@ Shortname: webxr
 Title: WebXR Device API
 Group: immersivewebwg
 Status: w3c/ED
+<<<<<<< HEAD
 TR: https://www.w3.org/TR/webxr/
+=======
+>>>>>>> Address feedback from nell
 ED: https://immersive-web.github.io/webxr/
 Repository: immersive-web/webxr
 Level: 1
@@ -585,7 +588,7 @@ An {{XRFrame}} represents a snapshot of the state of all of the tracked objects
 [SecureContext, Exposed=Window] interface XRFrame {
   readonly attribute XRSession session;
 
-  XRViewerPose? getViewerPose(optional XRReferenceSpace referenceSpace);
+  XRViewerPose? getViewerPose(XRReferenceSpace referenceSpace);
   XRPose? getPose(XRSpace space, XRSpace relativeTo);
 };
 </pre>
@@ -600,7 +603,7 @@ When the <dfn method for="XRFrame">getViewerPose(|referenceSpace|)</dfn> method
 
   1. If the {{XRFrame}}'s [=active=] boolean is <code>false</code>, throw a {{InvalidStateError}} and abort these steps.
   1. Let |session| be the {{XRFrame}}'s {{XRFrame/session}} object.
-  1. If |referenceSpace|'s [=XRSpace/session=] does not equal |session|, return <code>null</code> and abort these steps.
+  1. If |referenceSpace|'s [=XRSpace/session=] does not equal |session|, throw a {{InvalidStateError}} and abort these steps.
   1. If the [=viewer=]'s pose cannot be determined relative to |referenceSpace|, return <code>null</code>
   1. Return a new {{XRViewerPose}} describing the [=viewer=]'s pose relative to the origin of |referenceSpace| at the timestamp of the {{XRFrame}}.
 
@@ -612,15 +615,13 @@ When the <dfn method for="XRFrame">getPose(|space|, |relativeTo|)</dfn> method i
 
   1. If the {{XRFrame}}'s [=active=] boolean is <code>false</code>, throw a {{InvalidStateError}} and abort these steps.
   1. Let |session| be the {{XRFrame}}'s {{XRFrame/session}} object.
-  1. If |space|'s [=XRSpace/session=] does not equal |session|, return <code>null</code> and abort these steps.
-  1. If |relativeTo|'s [=XRSpace/session=] does not equal |session|, return <code>null</code> and abort these steps.
+  1. If |space|'s [=XRSpace/session=] does not equal |session|, throw a {{InvalidStateError}} and abort these steps.
+  1. If |relativeTo|'s [=XRSpace/session=] does not equal |session|, throw a {{InvalidStateError}} and abort these steps.
   1. If |space|'s pose cannot be determined relative to |relativeTo|, return <code>null</code>
   1. Return a new {{XRPose}} describing |space|'s pose relative to the origin of |relativeTo|.
 
 </div>
 
-Issue: Describe behavior for passing <code>null</code> {{XRReferenceSpace}}s to {{getViewerPose()}} and {{getPose()}}
-
 ISSUE: The last two steps of the {{getViewerPose()}} and {{getPose()}} algorithms need to be expanded.
 
 Spaces {#spaces}
@@ -951,7 +952,7 @@ An {{XRPose}} describes a position and orientation in space relative to an {{XRS
 
 The <dfn attribute for="XRPose">transform</dfn> attribute describes the {{XRRigidTransform}} between two {{XRSpace}}.
 
-The <dfn attribute for="XRPose">emulatedPosition</dfn> attribute indicates the accuracy of the {{XRPose/transform}}.{{XRRigidTransform/position}} value. {{XRPose/emulatedPosition}} MUST be set to <code>true</code> if the given positional values are software estimations, such as those provided by a neck or arm model. {{XRPose/emulatedPosition}} MUST be set to <code>false</code> if the positional values are based on sensor readings.
+The <dfn attribute for="XRPose">emulatedPosition</dfn> attribute MUST be <code>false</code> if the {{XRPose/transform}}.{{XRRigidTransform/position}} values are based on sensor readings, or <code>true</code> if the position values are software estimations, such as those provided by a neck or arm model. 
 
 XRViewerPose {#xrviewerpose-interface}
 -------------
@@ -1012,9 +1013,9 @@ Note: Some input sources, like an {{XRInputSource}} with {{targetRayMode}} set t
 
 The <dfn attribute for="XRInputSource">targetRaySpace</dfn> attribute is an {{XRSpace}} that tracks the pose of the preferred pointing ray of the {{XRInputSource}}, as defined by the {{targetRayMode}}.
 
-The <dfn attribute for="XRInputSource">gripSpace</dfn> attribute is an {{XRSpace}} that tracks the transform that should be used to render virtual objects such that they appear to be held in the user's hand. If the user were to hold a straight rod, this {{XRSpace}} places the origin at the centroid of their curled fingers and where the <code>-Z</code> axis points along the length of the rod towards their thumb. The <code>X</code> axis is perpendicular to the back of the hand being described, with back of the users right hand pointing towards <code>+X</code> and the back of the user's left hand pointing towards <code>-X</code>. The <code>Y</code> axis is implied by the relationship between the <code>X</code> and <code>Z</code> axis, with <code>+Y</code> roughly pointing in the direction of the user's arm.
+The <dfn attribute for="XRInputSource">gripSpace</dfn> attribute is an {{XRSpace}} that tracks the pose that should be used to render virtual objects such that they appear to be held in the user's hand. If the user were to hold a straight rod, this {{XRSpace}} places the origin at the centroid of their curled fingers and where the <code>-Z</code> axis points along the length of the rod towards their thumb. The <code>X</code> axis is perpendicular to the back of the hand being described, with back of the users right hand pointing towards <code>+X</code> and the back of the user's left hand pointing towards <code>-X</code>. The <code>Y</code> axis is implied by the relationship between the <code>X</code> and <code>Z</code> axis, with <code>+Y</code> roughly pointing in the direction of the user's arm.
 
-The {{gripSpace}} MUST be `null` if the input source isn't trackable.
+The {{gripSpace}} MUST be `null` if the input source isn't inherently trackable.
 
 Layers {#layers}
 ======
