Ensure initial about:blank Doc's initialness is not carried over

html/browsers/browsing-the-web/navigating-across-documents/initial-empty-document/iframe-nosrc.html

@@ -175,4 +175,39 @@
   assert_equals(history.length, startingHistoryLength + 1,
     "history.length increases after normal navigation from  non-initial empty document");
 }, "form submission");
+
+// This test is very similar to the `location.href` test a few cases above, but
+// the difference is that instead of navigating from:
+//   initial about:blank Document => HTTP => HTTP
+// ... we navigate from:
+//   initial about:blank Document => (non-initial) about:blank Document => HTTP
+//
+// We do this to ensure/assert that an explicit navigation to about:blank
+// *after* the iframe has finished initializing, is counted as a normal
+// navigation away from the initial about:blank Document, and the "initial-ness"
+// of the initial about:blank Document is not carried over to the next
+// about:blank Document.
+promise_test(async t => {
+  const startingHistoryLength = history.length;
+  // Create an iframe with src not set, which will stay on the initial empty
+  // document.
+  const iframe = insertIframe(t);
+  assert_equals(history.length, startingHistoryLength,
+    "Inserting iframe with no src must not change history.length");
+
+  // Navigate away from the initial empty document through setting location.href
+  // to `about:blank`. This should do a replacement TO ANOTHER about:blank
+  // Document, which is not the initial about:blank Document.
+  iframe.contentWindow.location.href = 'about:blank';
+  await waitForLoad(t, iframe, 'about:blank');
+  assert_equals(history.length, startingHistoryLength,
+    "history.length must not change after normal navigation on document loaded by iframe with no src");
+
+  // Navigate again using the same method, but this time it shouldn't do a
+  // replacement since it's no longer on the initial empty document.
+  iframe.contentWindow.location.href = url2;
+  await waitForLoad(t, iframe, url2);
+  assert_equals(history.length, startingHistoryLength + 1,
+    "history.length increases after normal navigation from  non-initial empty document");
+}, "initial about:blank => non-initial about:blank (via location.href) => normal HTTP navigation");
 </script>

html/browsers/browsing-the-web/navigating-across-documents/initial-empty-document/iframe-src-aboutblank-navigate-immediately.html

@@ -16,32 +16,42 @@
 
 promise_test(async t => {
   const startingHistoryLength = history.length;
-  // Create an iframe with src set to about:blank. This would trigger a
-  // navigation to a non-initial about:blank document.
+  // Create an iframe with src set to about:blank. Per the HTML Standard, this
+  // stays on the "initial about:blank Document" [1], because the "process the
+  // iframe attributes" algorithm [2] catches the "about:blank" navigation and
+  // fires a special synchronous `load` event at the initial about:blank
+  // Document, instead of replacing it with a non-initial, second about:blank
+  // Document. This is documented in the note at the end of [3].
+  //
+  // [1]: https://html.spec.whatwg.org/#is-initial-about:blank.
+  // [2]: https://html.spec.whatwg.org/#process-the-iframe-attributes
+  // [3]: https://html.spec.whatwg.org/#completely-finish-loading
   const iframe = insertIframeWithAboutBlankSrc(t);
   assert_equals(history.length, startingHistoryLength,
     "Inserting iframe with src='about:blank' must not change history.length");
 
-  // Trigger a navigation to url1 through the iframe's src attribute.
-  // The iframe should still be on the initial empty document, and the
-  // navigation should do replacement.
+  // Trigger a navigation from the initial about:blank Document, to url1 through
+  // the iframe's src attribute. Because we're navigating from the initial
+  // about:blank Document, the navigation should be a replacement.
   iframe.src = url1;
+
   // Wait for the latest navigation to finish.
   await waitForLoad(t, iframe, url1);
   assert_equals(history.length, startingHistoryLength,
-    "history.length must not change after normal navigation on initial empty document");
-}, "Navigating to a different document with src");
+    "history.length must not change after normal navigation from initial " +
+    "about:blank Document");
+}, "Navigating away from the initial about:blank Document to a different " +
+    "one, with src");
 
 promise_test(async t => {
   const startingHistoryLength = history.length;
-  // Create an iframe with src set to about:blank but navigate away from it immediately below.
   const iframe = insertIframeWithAboutBlankSrc(t);
   assert_equals(history.length, startingHistoryLength,
     "Inserting iframe with src='about:blank' must not change history.length");
 
-  // Navigate away from the initial empty document through setting
-  // location.href. The iframe should still be on the initial empty document,
-  // and the navigation should do replacement.
+  // Trigger a navigation from the initial about:blank Document, to url1 through
+  // location.href. Because we're navigating from the initial about:blank
+  // Document, the navigation should be a replacement.
   iframe.contentWindow.location.href = url1;
   await waitForLoad(t, iframe, url1);
   assert_equals(history.length, startingHistoryLength,
@@ -50,14 +60,13 @@
 
 promise_test(async t => {
   const startingHistoryLength = history.length;
-  // Create an iframe with src set to about:blank but navigate away from it immediately below.
   const iframe = insertIframeWithAboutBlankSrc(t);
   assert_equals(history.length, startingHistoryLength,
     "Inserting iframe with src='about:blank' must not change history.length");
 
-  // Navigate away from the initial empty document through location.assign().
-  // The iframe should still be on the initial empty document, and the
-  // navigation should do replacement.
+  // Trigger a navigation from the initial about:blank Document, to url1 through
+  // location.assign(). Because we're navigating from the initial about:blank
+  // Document, the navigation should be a replacement.
   iframe.contentWindow.location.assign(url1);
   await waitForLoad(t, iframe, url1);
   assert_equals(history.length, startingHistoryLength,
@@ -66,14 +75,13 @@
 
 promise_test(async t => {
   const startingHistoryLength = history.length;
-  // Create an iframe with src set to about:blank but navigate away from it immediately below.
   const iframe = insertIframeWithAboutBlankSrc(t);
   assert_equals(history.length, startingHistoryLength,
     "Inserting iframe with src='about:blank' must not change history.length");
 
-  // Navigate away from the initial empty document through window.open().
-  // The iframe should still be on the initial empty document, and the
-  // navigation should do replacement.
+  // Trigger a navigation from the initial about:blank Document, to url1 through
+  // window.open(). Because we're navigating from the initial about:blank
+  // Document, the navigation should be a replacement.
   iframe.contentWindow.open(url1, "_self");
   await waitForLoad(t, iframe, url1);
   assert_equals(history.length, startingHistoryLength,
@@ -82,14 +90,13 @@
 
 promise_test(async t => {
   const startingHistoryLength = history.length;
-  // Create an iframe with src set to about:blank but navigate away from it immediately below.
   const iframe = insertIframeWithAboutBlankSrc(t);
   assert_equals(history.length, startingHistoryLength,
     "Inserting iframe with src='about:blank' must not change history.length");
 
-  // Navigate away from the initial empty document through clicking an <a>
-  // element. The iframe should still be on the initial empty document, and the
-  // navigation should do replacement.
+  // Trigger a navigation from the initial about:blank Document, to url1 through
+  // clicking an `<a>` element. Because we're navigating from the initial
+  // about:blank Document, the navigation should be a replacement.
   const a = iframe.contentDocument.createElement("a");
   a.href = url1;
   iframe.contentDocument.body.appendChild(a);
@@ -101,14 +108,13 @@
 
 promise_test(async t => {
   const startingHistoryLength = history.length;
-  // Create an iframe with src set to about:blank but navigate away from it immediately below.
   const iframe = insertIframeWithAboutBlankSrc(t);
   assert_equals(history.length, startingHistoryLength,
     "Inserting iframe with src='about:blank' must not change history.length");
 
-  // Navigate away from the initial empty document through form submission.
-  // The iframe should still be on the initial empty document, and the
-  // navigation should do replacement.
+  // Trigger a navigation from the initial about:blank Document, to url1 through
+  // a form submission. Because we're navigating from the initial about:blank
+  // Document, the navigation should be a replacement.
   const form = iframe.contentDocument.createElement("form");
   form.action = "/common/blank.html";
   iframe.contentDocument.body.appendChild(form);

html/browsers/browsing-the-web/navigating-across-documents/initial-empty-document/resources/helpers.js

@@ -37,7 +37,16 @@ window.insertIframeWith204Src = (t) => {
   return iframe;
 };
 
-// Creates an iframe with src="about:blank" and appends it to the document.
+// Creates an iframe with src="about:blank" and appends it to the document. The
+// resulting document in the iframe is the initial about:blank Document [1],
+// because during the "process the iframe attributes" algorithm [2], `src`
+// navigations to `about:blank` are caught and result in a synchronous load
+// event; not a SEPARATE navigation to a non-initial `about:blank` Document. See
+// the documentation in [3] as well.
+//
+// [1]: https://html.spec.whatwg.org/#is-initial-about:blank
+// [2]: https://html.spec.whatwg.org/#process-the-iframe-attributes
+// [3]: https://html.spec.whatwg.org/#completely-finish-loading
 window.insertIframeWithAboutBlankSrc = (t) => {
   const iframe = document.createElement("iframe");
   t.add_cleanup(() => iframe.remove());
@@ -47,12 +56,14 @@ window.insertIframeWithAboutBlankSrc = (t) => {
 };
 
 // Creates an iframe with src="about:blank", appends it to the document, and
-// waits for the non-initial about:blank document finished loading.
+// waits for initial about:blank Document to finish loading.
 window.insertIframeWithAboutBlankSrcWaitForLoad = async (t) => {
   const iframe = insertIframeWithAboutBlankSrc(t);
   const aboutBlankLoad = new Promise(resolve => {
-    // In some browsers, the non-initial about:blank navigation commits
+    // In some browsers, when the initial about:blank Document is influenced by
+    // a `src=about:blank` attribute, the about:blank navigation commits
     // asynchronously, while in other browsers, it would commit synchronously.
+    //
     // This means we can't wait for the "load" event as it might have already
     // ran. Instead, just wait for 100ms before resolving, as the non-initial
     // about:blank navigation will most likely take less than 100 ms to commit.