Make Permissions-Policy HTTP header OPTIONAL (#275)

* Make Permissions-Policy HTTP header OPTIONAL

* Update index.html

Co-authored-by: Thomas Steiner <[email protected]>

* Update index.html

An editorial fix (the word "issues" was implied but missing), and rewrite last sentence of future spec expectations to improve grammar, remove use of a passive "mandatory" phrase. Feel free to revise that sentence further.

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Co-authored-by: Thomas Steiner <[email protected]>
Co-authored-by: Tantek Çelik <[email protected]>

Author: 3 people

index.html

@@ -716,6 +716,10 @@ <h2>
         allowlist/'self'=], which means third-party contexts are not [=allowed
         to use=] the API by default.
       </p>
+      <p>
+        It is OPTIONAL for user agents to support
+        [[[PERMISSIONS-POLICY]]]'s `Permissions-Policy` HTTP header.
+      </p>
       <p>
         Developers can use the means afforded by the [[[permissions-policy]]]
         specification to control if and when a third-party context is [=allowed
@@ -725,7 +729,7 @@ <h2>
         <p>
           Although user agents are unified in preventing the Web Share API from
           being used in third-party context, at the time of publication there
-          are interoperability with relying on the [[[Permissions-Policy]]] to
+          are interoperability issues with relying on the [[[Permissions-Policy]]] to
           enable the API in third-party contexts. In particular, although
           the[^iframe/allow^] attribute is widely supported, the updated syntax
           for the [^iframe/allow^] attribute is not. Similarly, the
@@ -734,6 +738,11 @@ <h2>
           [[[Permissions-Policy]]] specification before relying on it to enable
           the Web Share API in third-party contexts.
         </p>
+        <p>
+          When the `Permissions-Policy` HTTP header is more widely supported, 
+          the Working Group expects to revise this specification 
+          to require support for the header.
+        </p>
       </aside>
     </section>
     <section class="informative" id="a11y">