Correct management of sandboxing flag sets

Replaces ambiguous references to a browsing context property named
"sandboxing flag set".

Closes whatwg#5682.

source

@@ -80151,7 +80151,8 @@ interface <dfn>BarProp</dfn> {
   <p>Every <span>top-level browsing context</span> has a <dfn>popup sandboxing flag set</dfn>, which
   is a <span>sandboxing flag set</span>. When a <span>browsing context</span> is created, its
   <span>popup sandboxing flag set</span> must be empty. It is populated by <span>the rules for
-  choosing a browsing context</span>.</p>
+  choosing a browsing context</span> and the <span data-x="obtain-browsing-context-navigation">obtain
+  a browsing context to use for a navigation response</span> algorithm.</p>
 
   <p>Every <code>iframe</code> element has an <dfn><code>iframe</code> sandboxing flag set</dfn>,
   which is a <span>sandboxing flag set</span>. Which flags in an <span><code>iframe</code>
@@ -80384,8 +80385,11 @@ interface <dfn>BarProp</dfn> {
      <li><p>Assert: <var>navigationCOOP</var> is "<code
      data-x="coop-unsafe-none">unsafe-none</code>".</p></li>
 
-     <li><p>Set <var>newBrowsingContext</var>'s <span>sandboxing flag set</span> to
-     <var>sandboxFlags</var>.</p></li>
+     <li><p>Assert: <var>newBrowsingContext</var>'s <span>popup sandboxing flag set</span>
+     <span data-x="list is empty">is empty</span>.</p></li>
+
+     <li><p>Set <var>newBrowsingContext</var>'s <span>popup sandboxing flag set</span> to
+     a <span data-x="list clone">clone</span> of <var>sandboxFlags</var>.</p></li>
     </ol>
    </li>
 
@@ -82496,8 +82500,8 @@ interface <dfn>Location</dfn> { // but see also <a href="#the-location-interface
             close to reality its current definition is. -->
 
        <li><p>Let <var>finalSandboxFlags</var> be the union of <var>browsingContext</var>'s
-       <span>sandboxing flag set</span> and <var>resource</var>'s <span>forced sandboxing flag
-       set</span>.</p></li>
+       <span data-x="concept-bc-sandboxing-flags">sandboxing flags</span> and <var>resource</var>'s
+       <span>forced sandboxing flag set</span>.</p></li>
 
        <li><p>Let <var>responseOrigin</var> be the result of <span>determining the origin</span>
        given <var>browsingContext</var>, <var>resource</var>'s <span
@@ -82531,8 +82535,8 @@ interface <dfn>Location</dfn> { // but see also <a href="#the-location-interface
        browsing context</span>, and <var>browsingContext</var>.</p></li>
 
        <li><p>Let <var>finalSandboxFlags</var> be the union of <var>browsingContext</var>'s
-       <span>sandboxing flag set</span> and <var>response</var>'s <span>forced sandboxing flag
-       set</span>.</p></li>
+       <span data-x="concept-bc-sandboxing-flags">sandboxing flags</span> and <var>response</var>'s
+       <span>forced sandboxing flag set</span>.</p></li>
 
        <li><p>Run <span>process a navigate response</span> with <var>resource</var>,
        <var>response</var>, <var>navigationType</var>, the <span>source browsing context</span>,
@@ -82731,8 +82735,8 @@ interface <dfn>Location</dfn> { // but see also <a href="#the-location-interface
        result.</p></li>
 
        <li><p>Set <var>finalSandboxFlags</var> to the union of <var>browsingContext</var>'s
-       <span>sandboxing flag set</span> and <var>response</var>'s <span>forced sandboxing flag
-       set</span>.</p></li>
+       <span data-x="concept-bc-sandboxing-flags">sandboxing flags</span> and <var>response</var>'s
+       <span>forced sandboxing flag set</span>.</p></li>
 
        <li><p>Set <var>responseOrigin</var> to the result of <span>determining the origin</span>
        given <var>browsingContext</var>, <var>request's</var> <span