Clarify the conditions to expose sensor readings

This patch consolidates all the necessary conditions to
expose sensor readings to a single list at
https://w3c.github.io/sensors/#can-expose-sensor-readings
in order to make them more explicit and improve readability.

It also brings clarifications to the Sensor model description
and minor editorial changes (corrected references to the definitions
from the PERMISSIONS specification).

index.bs

@@ -75,6 +75,10 @@ urlPrefix: https://wicg.github.io/feature-policy/; spec: FEATURE-POLICY
     text: feature name
     text: policy-controlled feature
     text: allowed to use
+urlPrefix: https://www.w3.org/TR/permissions; spec: PERMISSIONS
+  type: dfn
+    text: permission name
+    text: permission state
 </pre>
 <pre class=link-defaults>
 spec: webidl; type:dfn; text:attribute
@@ -744,9 +748,14 @@ never exceed the [=sampling frequency=] for the given [=sensor type=].
 ## Conditions to expose sensor readings ## {#concepts-can-expose-sensor-readings}
 
 The user agent must verify that all [=mandatory conditions=] are satisfied to ensure it
-<dfn>can expose sensor readings</dfn> to a given [=active document=].
+<dfn>can expose sensor readings</dfn> to the {{Sensor}} objects of a certain
+[=sensor type|type=] that belong to a certain [=active document=].
 
 The <dfn>mandatory conditions</dfn> are the following:
+ - The given document is a [=responsible document=] of a [=secure context=].
+ - For each [=permission name=] from the [=sensor type=]'s associated
+   [=sensor permission names=] [=ordered set|set=], the corresponding permission's
+   [=permission state|state=] is "granted".
  - [=document visibility state|Visibility state=] of the document is "visible".
  - The document is [=allowed to use=] all the [=policy-controlled features=] associated
    with the given [=sensor type=].
@@ -771,9 +780,9 @@ A [=sensor type=] has a [=ordered set|set=] of <dfn export>associated sensors</d
 A [=sensor type=] may have a [=default sensor=].
 
 A [=sensor type=] has a [=set/is empty|nonempty=] [=ordered set|set=] of associated
-{{PermissionName|PermissionNames}} referred as <dfn export>sensor permission names</dfn>.
+[=permission names=] referred to as <dfn export>sensor permission names</dfn>.
 
-Note: multiple [=sensor types=] may share the same {{PermissionName}}.
+Note: multiple [=sensor types=] may share the same [=permission name=].
 
 A [=sensor type=] has a [=permission revocation algorithm=].
 
@@ -788,25 +797,23 @@ A [=sensor type=] has a [=permission revocation algorithm=].
 </div>
 
 A [=sensor type=] has a [=set/is empty|nonempty=] [=ordered set|set=] of associated
-[=feature names=] referred as <dfn export>sensor feature names</dfn>.
+[=feature names=] referred to as <dfn export>sensor feature names</dfn>.
 
 <h3 id="model-sensor">Sensor</h3>
 
-A [=platform sensor=] has an associated [=ordered set|set=]
-of <dfn>activated sensor objects</dfn>.
-This set is initially [=set/is empty|empty=].
-
-The current [=browsing context=]'s [=platform sensor=] has an associated <dfn>latest reading</dfn>
-[=ordered map|map=] which holds the latest available [=sensor readings=].
+The current [=browsing context=]'s [=platform sensor=] has an associated [=ordered set|set=]
+of <dfn>activated sensor objects</dfn>, which is initially [=set/is empty|empty=] and an
+associated <dfn>latest reading</dfn> [=ordered map|map=], which holds the latest available [=sensor readings=].
 
-Note: User agents can share [=latest reading=] [=ordered map|map=] between different
+Note: User agents can share the [=latest reading=] [=ordered map|map=] and
+the [=activated sensor objects=] [=ordered set|set=] between different
 [=browsing context|contexts=] only if the [=origins=] of these contexts' [=active documents=]
 are [=same origin-domain=].
 
 Any time a new [=sensor reading=] for a [=platform sensor=] is obtained and if the user agent
 [=can expose sensor readings=] to the current [=browsing context=]'s [=active document=],
-[=update latest reading=] is invoked with the [=platform sensor=]
-and the [=sensor reading=] as arguments.
+the user agent invokes [=update latest reading=] with the [=platform sensor=] and
+the [=sensor reading=] as arguments.
 
 The [=latest reading=] [=ordered map|map=] contains an [=map/entry=] whose [=map/key=] is
 "timestamp" and whose [=map/value=] is a high resolution timestamp that estimates the
@@ -1637,8 +1644,8 @@ each [=sensor type=] in [=extension specifications=]:
     Its [=attributes=] which expose [=sensor readings=] are [=read only=] and
     their getters must return the result of invoking [=get value from latest reading=]
     with <strong>this</strong> and [=attribute=] [=identifier=] as arguments.
--   A {{PermissionName}}, if the [=sensor type=] is not representing
-    [=sensor fusion=] (otherwise, {{PermissionName|PermissionNames}}
+-   A [=permission name=], if the [=sensor type=] is not representing
+    [=sensor fusion=] (otherwise, [=permission names=]
     associated with the fusion source [=sensor types=] must be used).
 
 An [=extension specification=] may specify the following definitions
@@ -1655,8 +1662,8 @@ for each [=sensor types=]:
 <h3 id="permission-api">Extending the Permission API</h3>
 
 An implementation of the {{Sensor}} interface for each [=sensor type=] must protect its
-[=sensor reading|reading=] by associated {{PermissionName}} or {{PermissionDescriptor}}.
-A [=Low-level=] {{Sensor|sensor}} may use its interface name as a {{PermissionName}},
+[=sensor reading|reading=] by associated [=permission name=] or {{PermissionDescriptor}}.
+A [=Low-level=] {{Sensor|sensor}} may use its interface name as a [=permission name=],
 for instance, "gyroscope" or "accelerometer". [=sensor fusion|Fusion sensors=] must
 [=request permission to use|request permission to access=] each of the sensors that are
 used as a source of fusion.