Make 4.2 non-normative

Closes #256

index.html

@@ -287,27 +287,25 @@ <h3>
           Resources Included in the <a>PerformanceResourceTiming</a> Interface
         </h3>
         <p>
-          All resource [=Request=]s [=fetch=]ed by a non-null
-          [=request/client=] MUST be included as
+          This section is non-normative.
+        </p>
+        <p>
+          Resource [=Request=]s [=fetch=]ed by a non-null [=request/client=] should be included as
           <a>PerformanceResourceTiming</a> objects in the [=request/client=]'s
           [=environment settings object/global object=]'s <a data-cite=
           "PERFORMANCE-TIMELINE-2#performance-timeline">Performance
           Timeline</a>, unless excluded from the timeline as part of the
           [=fetch|fetching process=]. Resources that are retrieved from
           <a data-cite="HTML#relevant-application-cache">relevant application
-          caches</a> or local resources MUST be included as
+          caches</a> or local resources should also be included as
           <a>PerformanceResourceTiming</a> objects in the <a data-cite=
           "PERFORMANCE-TIMELINE-2#performance-timeline">Performance
           Timeline</a> [[PERFORMANCE-TIMELINE-2]]. Resources for which the
           [=fetch=] was initiated, but was later aborted (e.g. due to a network
-          error) MAY be included as <a>PerformanceResourceTiming</a> objects in
+          error) should be included as <a>PerformanceResourceTiming</a> objects in
           the <a data-cite=
           "PERFORMANCE-TIMELINE-2#performance-timeline">Performance
-          Timeline</a> and MUST contain initialized attribute values for
-          processed substeps of the [=fetch|fetching process=].
-        </p>
-        <p>
-          The rest of this section is non-normative.
+          Timeline</a>, with their start and end timing.
         </p>
         <p>
           Examples: