add iframe call and run in parallel

spec.bs

@@ -491,8 +491,8 @@ attribute.
 
   1. <p class=XXX>TODO: destroy the nested traversable.</p>
 
-  1. [=Recalculate the untrusted network status of all fenced frame descendants=] given the
-     {{Document}}'s [=node navigable=]'s [=navigable/top-level traversable=].
+  1. [=In parallel=], [=recalculate the untrusted network status of all fenced frame descendants=]
+     given the {{Document}}'s [=node navigable=]'s [=navigable/top-level traversable=].
 </div>
 
 The <dfn attribute for=HTMLFencedFrameElement>config</dfn> IDL attribute getter steps are to return
@@ -2075,6 +2075,14 @@ Several APIs specific to fenced frames are defined on the {{Fence}} interface.
            [=set/append=] |ancestorFencedRoot| to |navigablesWithNetworkChildren|.
 </div>
 
+<div algorithm=iframe-remove-patch>
+  When an <{iframe}> element is [=removed from a document=], the user agent must run the following
+  step:
+
+  1. [=In parallel=], [=recalculate the untrusted network status of all fenced frame descendants=]
+     given the {{Document}}'s [=node navigable=]'s [=navigable/top-level traversable=].
+</div>
+
 A user agent has an associated <dfn>network revocation nonce set</dfn>, which is a [=set=] of
 [=partition nonces=], and a <dfn>network revocation exemption map</dfn>, which is a [=map=] whose
 [=map/keys=] are [=partition nonces=] and [=map/values=] are [=sets=] of [=URLs=].