Change words to avoid normative requirements twice but make the meaning clear. Fixes #795.

Author: jungkees

spec/service_worker/index.html

@@ -3720,7 +3720,7 @@ <h1>Appendix B: Extended HTTP headers</h1>
 
   <spec-section id="service-worker-script-request">
     <h1>Service Worker Script Request</h1>
-    <p>An HTTP request to <a href="https://fetch.spec.whatwg.org/#concept-fetch">fetch</a> a <a href="#dfn-service-worker">service worker</a>'s <a href="#dfn-script-resource">script resource</a> <em class="rfc2119" title="MUST">must</em> include the following <a href="https://fetch.spec.whatwg.org/#concept-header">header</a>:</p>
+    <p>An HTTP request to <a href="https://fetch.spec.whatwg.org/#concept-fetch">fetch</a> a <a href="#dfn-service-worker">service worker</a>'s <a href="#dfn-script-resource">script resource</a> will include the following <a href="https://fetch.spec.whatwg.org/#concept-header">header</a>:</p>
 
     <dl>
       <dt>`<dfn><code>Service-Worker</code></dfn>`</dt>
@@ -3732,11 +3732,11 @@ <h1>Service Worker Script Request</h1>
 
   <spec-section id="service-worker-script-response">
     <h1>Service Worker Script Response</h1>
-    <p>An HTTP response to a <a href="#dfn-service-worker">service worker</a>'s <a href="#dfn-script-resource">script resource</a> request <em class="rfc2119" title="MAY">may</em> include the following <a href="https://fetch.spec.whatwg.org/#concept-header">header</a>:</p>
+    <p>An HTTP response to a <a href="#dfn-service-worker">service worker</a>'s <a href="#dfn-script-resource">script resource</a> request can include the following <a href="https://fetch.spec.whatwg.org/#concept-header">header</a>:</p>
 
     <dl>
       <dt>`<dfn><code>Service-Worker-Allowed</code></dfn>`</dt>
-      <dd>Indicates the user agent <em class="rfc2119" title="MUST">must</em> override the path restriction, which limits the maximum allowed <a href="#dfn-scope-url">scope url</a> that the script can <a href="#dfn-control">control</a>, to the given value.
+      <dd>Indicates the user agent will override the path restriction, which limits the maximum allowed <a href="#dfn-scope-url">scope url</a> that the script can <a href="#dfn-control">control</a>, to the given value.
         <p class="note">The value is a URL. If a relative URL is given, it is parsed against the script's URL.</p>
       </dd>
     </dl>

spec/service_worker_1/index.html

@@ -3718,7 +3718,7 @@ <h1>Appendix B: Extended HTTP headers</h1>
 
   <spec-section id="service-worker-script-request">
     <h1>Service Worker Script Request</h1>
-    <p>An HTTP request to <a href="https://fetch.spec.whatwg.org/#concept-fetch">fetch</a> a <a href="#dfn-service-worker">service worker</a>'s <a href="#dfn-script-resource">script resource</a> <em class="rfc2119" title="MUST">must</em> include the following <a href="https://fetch.spec.whatwg.org/#concept-header">header</a>:</p>
+    <p>An HTTP request to <a href="https://fetch.spec.whatwg.org/#concept-fetch">fetch</a> a <a href="#dfn-service-worker">service worker</a>'s <a href="#dfn-script-resource">script resource</a> will include the following <a href="https://fetch.spec.whatwg.org/#concept-header">header</a>:</p>
 
     <dl>
       <dt>`<dfn><code>Service-Worker</code></dfn>`</dt>
@@ -3730,11 +3730,11 @@ <h1>Service Worker Script Request</h1>
 
   <spec-section id="service-worker-script-response">
     <h1>Service Worker Script Response</h1>
-    <p>An HTTP response to a <a href="#dfn-service-worker">service worker</a>'s <a href="#dfn-script-resource">script resource</a> request <em class="rfc2119" title="MAY">may</em> include the following <a href="https://fetch.spec.whatwg.org/#concept-header">header</a>:</p>
+    <p>An HTTP response to a <a href="#dfn-service-worker">service worker</a>'s <a href="#dfn-script-resource">script resource</a> request can include the following <a href="https://fetch.spec.whatwg.org/#concept-header">header</a>:</p>
 
     <dl>
       <dt>`<dfn><code>Service-Worker-Allowed</code></dfn>`</dt>
-      <dd>Indicates the user agent <em class="rfc2119" title="MUST">must</em> override the path restriction, which limits the maximum allowed <a href="#dfn-scope-url">scope url</a> that the script can <a href="#dfn-control">control</a>, to the given value.
+      <dd>Indicates the user agent will override the path restriction, which limits the maximum allowed <a href="#dfn-scope-url">scope url</a> that the script can <a href="#dfn-control">control</a>, to the given value.
         <p class="note">The value is a URL. If a relative URL is given, it is parsed against the script's URL.</p>
       </dd>
     </dl>