feat: Editorial review: Add docs for notRestoredReasons (#32920)

* Adds docs for notRestoredReasons * Update files/en-us/web/api/performance_api/reporting_backforward_cache_not_restored_reasons/index.md Co-authored-by: Barry Pollard <barrypollard@google.com> * Update files/en-us/web/api/performance_api/reporting_backforward_cache_not_restored_reasons/index.md Co-authored-by: Barry Pollard <barrypollard@google.com> * Making fixes for review comments from tunetheweb and Josh-Cena * Add explainer link * Add content to explain NotRestoredReasons empty cases * Make small change to regenerate preview pages * Update content for final implementation of notRestoredReasons * Fixes for tunetheweb review comments * Update files/en-us/web/api/notrestoredreasons/index.md Co-authored-by: skyclouds2001 <95597335+skyclouds2001@users.noreply.github.com> * Update files/en-us/web/api/notrestoredreasondetails/index.md Co-authored-by: skyclouds2001 <95597335+skyclouds2001@users.noreply.github.com> * Update files/en-us/web/api/notrestoredreasons/index.md Co-authored-by: skyclouds2001 <95597335+skyclouds2001@users.noreply.github.com> * Update files/en-us/web/api/performancenavigationtiming/index.md Co-authored-by: skyclouds2001 <95597335+skyclouds2001@users.noreply.github.com> * Update files/en-us/web/api/notrestoredreasons/tojson/index.md Co-authored-by: skyclouds2001 <95597335+skyclouds2001@users.noreply.github.com> * Update files/en-us/web/api/notrestoredreasondetails/tojson/index.md Co-authored-by: skyclouds2001 <95597335+skyclouds2001@users.noreply.github.com> * Fix linter errors * Update files/en-us/web/api/performance_api/reporting_backforward_cache_not_restored_reasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/performance_api/reporting_backforward_cache_not_restored_reasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/performance_api/reporting_backforward_cache_not_restored_reasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/performance_api/reporting_backforward_cache_not_restored_reasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/performance_api/reporting_backforward_cache_not_restored_reasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/performance_api/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/performance_api/reporting_backforward_cache_not_restored_reasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/performance_api/reporting_backforward_cache_not_restored_reasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/performancenavigationtiming/notrestoredreasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/performancenavigationtiming/notrestoredreasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/performancenavigationtiming/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/reasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasondetails/reason/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasondetails/reason/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasondetails/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/performance_api/reporting_backforward_cache_not_restored_reasons/index.md Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com> * Fixes for Elchi3 review comments, bfcache glossary entry added * Update files/en-us/glossary/bfcache/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasondetails/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasondetails/reason/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasondetails/tojson/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/performancenavigationtiming/notrestoredreasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/src/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasondetails/reason/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/url/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/tojson/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/url/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/children/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/children/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/src/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/id/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/id/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/reasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/reasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/name/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/name/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * Update files/en-us/web/api/notrestoredreasons/reasons/index.md Co-authored-by: Florian Scholz <fs@florianscholz.com> * fix broken link * Add CC attribution note --------- Co-authored-by: Barry Pollard <barrypollard@google.com> Co-authored-by: skyclouds2001 <95597335+skyclouds2001@users.noreply.github.com> Co-authored-by: Florian Scholz <fs@florianscholz.com> Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
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diff --git a/files/en-us/glossary/bfcache/index.md b/files/en-us/glossary/bfcache/index.md
@@ -0,0 +1,19 @@
+---
+title: bfcache
+slug: Glossary/bfcache
+page-type: glossary-definition
+---
+
+{{GlossarySidebar}}
+
+The **back/forward** cache, or **bfcache**, is a performance-enhancing feature available in modern browsers that enables instant back and forward navigation between previously-visited pages. It does this by storing a complete snapshot of a page as the user navigates away from it; the browser can then quickly restore the snapshot if the user decides to return to it, rather than needing to repeat the network requests required to load the page.
+
+The snapshot contains the entire page in memory, including the JavaScript heap; in-progess code is paused when the user navigates away and resumed when they return to the page. A regular HTTP cache entry on the other hand contains only responses to previous requests. The bfcache therefore provides faster results than the HTTP cache.
+
+The downside is that bfcache entries require more resources, and create complexity in terms of how to represent in-progress code. Some code features (for example the [`unload`](/en-US/docs/Web/API/Window/unload_event) handler) are not compatible, so their presence on a page blocks it from using the bfcache.
+
+The bfcache is great for performance, so it is in your interests to make sure your pages are not blocked from using it. You can use the [`notRestoredReasons` API](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons) to monitor whether pages are blocked from using the bfcache, and reasons why.
+
+## See also
+
+- [Back and forward cache](https://web.dev/articles/bfcache) on web.dev (2023)
diff --git a/files/en-us/web/api/notrestoredreasondetails/index.md b/files/en-us/web/api/notrestoredreasondetails/index.md
@@ -0,0 +1,41 @@
+---
+title: NotRestoredReasonDetails
+slug: Web/API/NotRestoredReasonDetails
+page-type: web-api-interface
+status:
+  - experimental
+browser-compat: api.NotRestoredReasonDetails
+---
+
+{{APIRef("Performance API")}}{{SeeCompatTable}}
+
+The **`NotRestoredReasonDetails`** interface of the {{domxref("Performance API", "Performance API", "", "nocode")}} represents a single reason why a navigated page was blocked from using the back/forward cache ({{Glossary("bfcache")}}).
+
+An array of `NotRestoredReasonDetails` objects can be accessed via the {{domxref("NotRestoredReasons.reasons")}} property.
+
+## Instance properties
+
+- {{domxref("NotRestoredReasonDetails.reason", "reason")}} {{ReadOnlyInline}} {{Experimental_Inline}}
+  - : A string describing a reason that the page was blocked from using the back/forward cache.
+
+## Instance methods
+
+- {{domxref("NotRestoredReasonDetails.toJSON", "toJSON()")}} {{Experimental_Inline}}
+  - : A {{Glossary("Serialization","serializer")}}; returns a JSON representation of the `NotRestoredReasonDetails` object.
+
+## Examples
+
+See [Monitoring bfcache blocking reasons](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons) for examples.
+
+## Specifications
+
+{{Specifications}}
+
+## Browser compatibility
+
+{{Compat}}
+
+## See also
+
+- [Monitoring bfcache blocking reasons](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons)
+- {{domxref("PerformanceNavigationTiming.notRestoredReasons")}}
diff --git a/files/en-us/web/api/notrestoredreasondetails/reason/index.md b/files/en-us/web/api/notrestoredreasondetails/reason/index.md
@@ -0,0 +1,63 @@
+---
+title: "NotRestoredReasonDetails: reason property"
+short-title: reason
+slug: Web/API/NotRestoredReasonDetails/reason
+page-type: web-api-instance-property
+status:
+  - experimental
+browser-compat: api.NotRestoredReasonDetails.reason
+---
+
+{{APIRef("Performance API")}}{{SeeCompatTable}}
+
+The **`reason`** read-only property of the
+{{domxref("NotRestoredReasonDetails")}} interface returns a string describing a reason that the page was blocked from using the back/forward cache ({{Glossary("bfcache")}}).
+
+## Value
+
+A string.
+
+There are many different reasons why blocking could occur, and browsers can choose to implement their own specific reasons for blocking, based on how they operate. Developers should avoid depending on specific wording for reasons and be prepared to handle new reasons being added and deleted.
+
+The initial values listed in the specification are:
+
+- `"fetch"`
+  - : While unloading, a fetch initiated by the current document (e.g. via {{domxref("fetch()")}}) was canceled while ongoing. As a result, the page was not in a stable state that could be stored in the bfcache.
+- `"lock"`
+  - : While unloading, held locks and lock requests were terminated, so the page was not in a stable state that could be stored in the bfcache.
+- `"masked"`
+  - : The exact reason is hidden for privacy purposes. This value can mean one of the following:
+    - The current document has children contained in a cross-origin {{htmlelement("iframe")}}, and they prevented storage in the bfcache.
+    - The current Document could not be stored in the bfcache for user agent-specific reasons.
+- `"navigation-failure"`
+  - : The original navigation that created the current document errored, and storing the resulting error document in the bfcache was prevented.
+- `"parser-aborted"`
+  - : The current document never finished its initial HTML parsing, and storing the unfinished document in the bfcache was prevented.
+- `"websocket"`
+  - : While unloading, an open [WebSocket](/en-US/docs/Web/API/WebSockets_API) connect was shut down, so the page was not in a stable state that could be stored in the bfcache.
+
+Additional blocking reasons may be used by some browsers, for example:
+
+- `"unload-listener"`
+  - : The page registers an [`unload`](/en-US/docs/Web/API/Window/unload_event) handler, which prevents bfcache usage. This serves as a useful warning, as `unload` is deprecated. See [usage notes](/en-US/docs/Web/API/Window/unload_event#usage_notes) for more information.
+- `"response-cache-control-no-store"`
+  - : The page uses `no-store` as a {{httpheader("Cache-Control")}} header value.
+- `"related-active-contents"`
+  - : The page was opened from another page that still has a reference to this page, for example using "duplicate tab" functionality.
+
+## Examples
+
+See [Monitoring bfcache blocking reasons](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons) for examples.
+
+## Specifications
+
+{{Specifications}}
+
+## Browser compatibility
+
+{{Compat}}
+
+## See also
+
+- [Monitoring bfcache blocking reasons](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons)
+- {{domxref("PerformanceNavigationTiming.notRestoredReasons")}}
diff --git a/files/en-us/web/api/notrestoredreasondetails/tojson/index.md b/files/en-us/web/api/notrestoredreasondetails/tojson/index.md
@@ -0,0 +1,54 @@
+---
+title: "NotRestoredReasonDetails: toJSON() method"
+short-title: toJSON()
+slug: Web/API/NotRestoredReasonDetails/toJSON
+page-type: web-api-instance-method
+status:
+  - experimental
+browser-compat: api.NotRestoredReasonDetails.toJSON
+spec-urls: https://html.spec.whatwg.org/multipage/nav-history-apis.html#notrestoredreasondetails
+---
+
+{{APIRef("Performance API")}}{{SeeCompatTable}}
+
+The **`toJSON()`** method of the {{domxref("NotRestoredReasonDetails")}} interface is a {{Glossary("Serialization","serializer")}}; it returns a JSON representation of the {{domxref("NotRestoredReasonDetails")}} object.
+
+## Syntax
+
+```js-nolint
+toJSON()
+```
+
+### Parameters
+
+None.
+
+### Return value
+
+A {{jsxref("JSON")}} object that is the serialization of the {{domxref("NotRestoredReasonDetails")}} object.
+
+## Examples
+
+The following function will return a JSON representation of the first `NotRestoredReasonDetails` object of the `NotRestoredReasons` object from the first `PerformanceNavigationTiming` object currently present in the performance timeline:
+
+```js
+function returnNRR() {
+  const navEntries = performance.getEntriesByType("navigation");
+  let navEntry = navEntries[0];
+  return navEntry.notRestoredReasons.reasons[0].toJSON();
+}
+```
+
+## Specifications
+
+{{Specifications}}
+
+## Browser compatibility
+
+{{Compat}}
+
+## See also
+
+- {{jsxref("JSON")}}
+- [Monitoring bfcache blocking reasons](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons)
+- {{domxref("PerformanceNavigationTiming.notRestoredReasons")}}
diff --git a/files/en-us/web/api/notrestoredreasons/children/index.md b/files/en-us/web/api/notrestoredreasons/children/index.md
@@ -0,0 +1,39 @@
+---
+title: "NotRestoredReasons: children property"
+short-title: children
+slug: Web/API/NotRestoredReasons/children
+page-type: web-api-instance-property
+status:
+  - experimental
+browser-compat: api.NotRestoredReasons.children
+---
+
+{{APIRef("Performance API")}}{{SeeCompatTable}}
+
+The **`children`** read-only property of the
+{{domxref("NotRestoredReasons")}} interface returns an array of {{domxref("NotRestoredReasons")}} objects, one for each child {{htmlelement("iframe")}} embedded in the current document, which may contain reasons why the top-level frame was blocked relating to the child frames.
+
+Each object has the same structure as the parent object — this way, any number of levels of embedded `<iframe>`s can be represented inside the object recursively.
+
+## Value
+
+An array of {{domxref("NotRestoredReasons")}} objects.
+
+If the frame has no children, the array will be empty; if the document is in a cross-origin `<iframe>`, `children` will return `null`.
+
+## Examples
+
+See [Monitoring bfcache blocking reasons](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons) for examples.
+
+## Specifications
+
+{{Specifications}}
+
+## Browser compatibility
+
+{{Compat}}
+
+## See also
+
+- [Monitoring bfcache blocking reasons](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons)
+- {{domxref("PerformanceNavigationTiming.notRestoredReasons")}}
diff --git a/files/en-us/web/api/notrestoredreasons/id/index.md b/files/en-us/web/api/notrestoredreasons/id/index.md
@@ -0,0 +1,37 @@
+---
+title: "NotRestoredReasons: id property"
+short-title: id
+slug: Web/API/NotRestoredReasons/id
+page-type: web-api-instance-property
+status:
+  - experimental
+browser-compat: api.NotRestoredReasons.id
+---
+
+{{APIRef("Performance API")}}{{SeeCompatTable}}
+
+The **`id`** read-only property of the
+{{domxref("NotRestoredReasons")}} interface returns a string representing the `id` attribute value of the {{htmlelement("iframe")}} the document is contained in (for example `<iframe id="foo" src="...">`).
+
+## Value
+
+A string.
+
+If the document is not in an `<iframe>` or the `<iframe>` has no `id` set, `id` will return `null`.
+
+## Examples
+
+See [Monitoring bfcache blocking reasons](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons) for examples.
+
+## Specifications
+
+{{Specifications}}
+
+## Browser compatibility
+
+{{Compat}}
+
+## See also
+
+- [Monitoring bfcache blocking reasons](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons)
+- {{domxref("PerformanceNavigationTiming.notRestoredReasons")}}
diff --git a/files/en-us/web/api/notrestoredreasons/index.md b/files/en-us/web/api/notrestoredreasons/index.md
@@ -0,0 +1,51 @@
+---
+title: NotRestoredReasons
+slug: Web/API/NotRestoredReasons
+page-type: web-api-interface
+status:
+  - experimental
+browser-compat: api.NotRestoredReasons
+---
+
+{{APIRef("Performance API")}}{{SeeCompatTable}}
+
+The **`NotRestoredReasons`** interface of the {{domxref("Performance API", "Performance API", "", "nocode")}} provides report data containing reasons why the current document was blocked from using the back/forward cache ({{Glossary("bfcache")}}) on navigation.
+
+These objects are accessed via the {{domxref("PerformanceNavigationTiming.notRestoredReasons")}} property.
+
+## Instance properties
+
+- {{domxref("NotRestoredReasons.children", "children")}} {{ReadOnlyInline}} {{Experimental_Inline}}
+  - : An array of `NotRestoredReasons` objects, one for each child {{htmlelement("iframe")}} embedded in the current document, which may contain reasons why the top-level frame was blocked relating to the child frames. Each object has the same structure as the parent object — this way, any number of levels of embedded `<iframe>`s can be represented inside the object recursively. If the frame has no children, the array will be empty; if the document is in a cross-origin `<iframe>`, `children` will return `null`.
+- {{domxref("NotRestoredReasons.id", "id")}} {{ReadOnlyInline}} {{Experimental_Inline}}
+  - : A string representing the `id` attribute value of the `<iframe>` the document is contained in (for example `<iframe id="foo" src="...">`). If the document is not in an `<iframe>` or the `<iframe>` has no `id` set, `id` will return `null`.
+- {{domxref("NotRestoredReasons.name", "name")}} {{ReadOnlyInline}} {{Experimental_Inline}}
+  - : A string representing the `name` attribute value of the `<iframe>` the document is contained in (for example `<iframe name="bar" src="...">`). If the document is not in an `<iframe>` or the `<iframe>` has no `name` set, `name` will return `null`.
+- {{domxref("NotRestoredReasons.reasons", "reasons")}} {{ReadOnlyInline}} {{Experimental_Inline}}
+  - : An array of {{domxref("NotRestoredReasonDetails")}} objects, each representing a reason why the navigated page was blocked from using the bfcache. If the document is in a cross-origin `<iframe>`, `reasons` will return `null`, but the parent document may show a `reason` of `"masked"` if any `<iframe>`s blocked bfcache usage for the top-level frame.
+- {{domxref("NotRestoredReasons.src", "src")}} {{ReadOnlyInline}} {{Experimental_Inline}}
+  - : A string representing the path to the source of the `<iframe>` the document is contained in (for example `<iframe src="exampleframe.html">`). If the document is not in an `<iframe>`, `src` will return `null`.
+- {{domxref("NotRestoredReasons.url", "url")}} {{ReadOnlyInline}} {{Experimental_Inline}}
+  - : A string representing the URL of the navigated page or `<iframe>`. If the document is in a cross-origin `<iframe>`, `url` will return `null`.
+
+## Instance methods
+
+- {{domxref("NotRestoredReasons.toJSON", "toJSON()")}} {{Experimental_Inline}}
+  - : A {{Glossary("Serialization","serializer")}}; returns a JSON representation of the `NotRestoredReasons` object.
+
+## Examples
+
+See [Monitoring bfcache blocking reasons](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons) for examples.
+
+## Specifications
+
+{{Specifications}}
+
+## Browser compatibility
+
+{{Compat}}
+
+## See also
+
+- [Monitoring bfcache blocking reasons](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons)
+- {{domxref("PerformanceNavigationTiming.notRestoredReasons")}}
diff --git a/files/en-us/web/api/notrestoredreasons/name/index.md b/files/en-us/web/api/notrestoredreasons/name/index.md
@@ -0,0 +1,37 @@
+---
+title: "NotRestoredReasons: name property"
+short-title: name
+slug: Web/API/NotRestoredReasons/name
+page-type: web-api-instance-property
+status:
+  - experimental
+browser-compat: api.NotRestoredReasons.name
+---
+
+{{APIRef("Performance API")}}{{SeeCompatTable}}
+
+The **`name`** read-only property of the
+{{domxref("NotRestoredReasons")}} interface returns a string representing the `name` attribute value of the {{htmlelement("iframe")}} the document is contained in (for example `<iframe name="bar" src="...">`).
+
+## Value
+
+A string.
+
+If the document is not in an `<iframe>` or the `<iframe>` has no `name` set, `name` will return `null`.
+
+## Examples
+
+See [Monitoring bfcache blocking reasons](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons) for examples.
+
+## Specifications
+
+{{Specifications}}
+
+## Browser compatibility
+
+{{Compat}}
+
+## See also
+
+- [Monitoring bfcache blocking reasons](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons)
+- {{domxref("PerformanceNavigationTiming.notRestoredReasons")}}
diff --git a/files/en-us/web/api/notrestoredreasons/reasons/index.md b/files/en-us/web/api/notrestoredreasons/reasons/index.md
@@ -0,0 +1,37 @@
+---
+title: "NotRestoredReasons: reasons property"
+short-title: reasons
+slug: Web/API/NotRestoredReasons/reasons
+page-type: web-api-instance-property
+status:
+  - experimental
+browser-compat: api.NotRestoredReasons.reasons
+---
+
+{{APIRef("Performance API")}}{{SeeCompatTable}}
+
+The **`reasons`** read-only property of the
+{{domxref("NotRestoredReasons")}} interface returns an array of {{domxref("NotRestoredReasonDetails")}} objects, each representing a reason why the navigated page was blocked from using the back/forward cache ({{Glossary("bfcache")}}).
+
+## Value
+
+An array of {{domxref("NotRestoredReasonDetails")}} objects. See [Blocking reasons](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons#blocking_reasons) for a list of the possible blocking reasons.
+
+If the document is in a cross-origin {{htmlelement("iframe")}}, `reasons` will return `null`, but the parent document may show a `reason` of `"masked"` if any `<iframe>`s blocked bfcache usage for the top-level frame.
+
+## Examples
+
+See [Monitoring bfcache blocking reasons](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons) for examples.
+
+## Specifications
+
+{{Specifications}}
+
+## Browser compatibility
+
+{{Compat}}
+
+## See also
+
+- [Monitoring bfcache blocking reasons](/en-US/docs/Web/API/Performance_API/Monitoring_bfcache_blocking_reasons)
+- {{domxref("PerformanceNavigationTiming.notRestoredReasons")}}