editorial: Use navigables, not browsing contexts, in CSS media feature (

#119)

Related to #104.

The end result is the same, but we now avoid using deprecated terms. The
text has also been simplified: saying that something applies to the
top-level browsing context and all child contexts is redundant (it basically
says it applies to all pages); the relevant point which is that navigables
that are not top-level traversables reflect the latter's value, has been
kept.

index.html

@@ -340,10 +340,9 @@ <h3>
       </h3>
       <p>
         The <code><dfn>device-posture</dfn></code> media feature represents,
-        via a CSS media query [[MEDIAQ]], the <a>posture</a> of the device.
-        This media feature applies to the top-level browsing context and any
-        child browsing contexts. Child browsing contexts reflect the
-        <a>posture</a> of the <a>top-level browsing context</a>.
+        via a CSS media query [[MEDIAQ]], the <a>posture</a> of the device. All
+        <a>navigables</a> reflect the <a>posture</a> of their
+        [=navigable/top-level traversable=].
       </p>
       <dl>
         <dt>