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Lighthouse Mobile

· 0 checks — Mobile Lighthouse audit -- Performance, Accessibility, Best Practices, and SEO category breakdown.
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Detailed Report

Audit breakdown by category with detailed findings.

34

Performance

Insights

Remove large, duplicate JavaScript modules from bundles to reduce unnecessary bytes consumed by network activity.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Polyfills and transforms enable older browsers to use new JavaScript features. However, many aren't necessary for modern browsers. Consider modifying your JavaScript build process to not transpile Baseline features, unless you know you must support older browsers. Learn why most sites can deploy ES6+ code without transpiling

Why this matters

Performance issues directly impact user engagement and conversion rates.

3rd party code can significantly impact load performance. Reduce and defer loading of 3rd party code to prioritize your page's content.

Why this matters

Performance issues directly impact user engagement and conversion rates.

A long cache lifetime can speed up repeat visits to your page. Learn more about caching.

Why this matters

Performance issues directly impact user engagement and conversion rates.

RequestCache TTLTransfer Size
consent.cookiebot.com/Framework/IAB/consent-sdk-2.3.js149.0 s87.9 KiB
consent.cookiebot.com/uc.js663.0 s35.7 KiB
/cdn-cgi/challenge-platform/h/b/scripts/jsd/0b8fb825cb67/...14400.0 s13.7 KiB
bmwebsitestreaming.blob.core.windows.net/bmvideo/Tour_of_the_British_Museum.mp40.0 ms0 B

A forced reflow occurs when JavaScript queries geometric properties (such as offsetWidth) after styles have been invalidated by a change to the DOM state. This can result in poor performance. Learn more about forced reflows and possible mitigations.

Why this matters

Performance issues directly impact user engagement and conversion rates.

headings: [map[key:source label:Source valueType:source-location] map[granularity:1 key:reflowTime label:Total reflow time valueType:ms]]
items: [map[reflowTime:17.31 source:map[type:text value:[unattributed]]] map[reflowTime:18.857 source:map[column:91010 line:1 type:source-location url:https://www.britishmuseum.org/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vHJjaeoQR8pPIOk.js?scope=footer&delta=4&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkw urlProvider:network]] map[reflowTime:0.642 source:map[column:233587 line:1 type:source-location url:https://www.britishmuseum.org/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vHJjaeoQR8pPIOk.js?scope=footer&delta=4&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkw urlProvider:network]] map[reflowTime:4.218 source:map[column:261248 line:1 type:source-location url:https://www.britishmuseum.org/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vHJjaeoQR8pPIOk.js?scope=footer&delta=4&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkw urlProvider:network]] map[reflowTime:2.646 source:map[column:255685 line:1 type:source-location url:https://www.britishmuseum.org/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vHJjaeoQR8pPIOk.js?scope=footer&delta=4&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkw urlProvider:network]] map[reflowTime:1.526 source:map[column:267273 line:1 type:source-location url:https://www.britishmuseum.org/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vHJjaeoQR8pPIOk.js?scope=footer&delta=4&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkw urlProvider:network]] map[reflowTime:0.428 source:map[column:304434 line:1 type:source-location url:https://www.britishmuseum.org/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vHJjaeoQR8pPIOk.js?scope=footer&delta=4&language=en&theme=numiko&include=eJzLK83NzM7XT8_JT0rM0S1OLsosKCnWycMmqpuRmpiSWgQA9VcTkw urlProvider:network]]]

Reducing the download time of images can improve the perceived load time of the page and LCP. Learn more about optimizing image size

Why this matters

Performance issues directly impact user engagement and conversion rates.

URLResource SizeEst Savings
A wide shot of the Great Court with the roof and Reading Room in view div.hero__background > div.media > picture > img
/sites/default/files/styles/1_1_media_small/public/2019-1...101.1 KiB49.8 KiB
Section of the Bayeux Tapestry showing a group of warriors with shields and spe… div.teaser__image-container > div.media > picture > img
/sites/default/files/styles/16_9_media_small/public/2026-...80.7 KiB42.3 KiB
A close up of a section of a feathered Hawai'ian cloak showing yellow and black… div.teaser__image-container > div.media > picture > img
/sites/default/files/styles/16_9_media_small/public/2025-...77.3 KiB38.9 KiB

Optimize LCP by making the LCP image discoverable from the HTML immediately, and avoiding lazy-loading

Why this matters

Performance issues directly impact user engagement and conversion rates.

lhId: page-3-VIDEO
nodeLabel: main#main-content > div > div.hero--front > video#hero-video
path: 1,HTML,1,BODY,5,DIV,4,DIV,0,DIV,2,MAIN,0,DIV,0,DIV,1,VIDEO
selector: main#main-content > div > div.hero--front > video#hero-video
snippet: <video class="hero__video" id="hero-video" data-js-video-background="" disablepictureinpicture="" playsinline="" autoplay="" muted="" loop="">

Avoid chaining critical requests by reducing the length of chains, reducing the download size of resources, or deferring the download of unnecessary resources to improve page load.

Why this matters

Performance issues directly impact user engagement and conversion rates.

description: [preconnect](https://developer.chrome.com/docs/lighthouse/performance/uses-rel-preconnect/) hints help the browser establish a connection earlier in the page load, saving time when the first request for that origin is made. The following are the origins that the page preconnected to.
title: Preconnected origins
description: Add [preconnect](https://developer.chrome.com/docs/lighthouse/performance/uses-rel-preconnect/) hints to your most important origins, but try to use no more than 4.
title: Preconnect candidates

Requests are blocking the page's initial render, which may delay LCP. Deferring or inlining can move these network requests out of the critical path.

Why this matters

Performance issues directly impact user engagement and conversion rates.

URLTransfer SizeDuration
/sites/default/files/css/css_qv6dCFGN2Vda1nUS7_s-LrSxyqnB...44.3 KiB773 ms
/sites/default/files/js/js_SLwwA2J3XCQ_1HHbqjZARtcKpH5ptr...1.3 KiB473 ms
/sites/default/files/css/css_VsHlxZe888vVcIftkt15QWpKH3V1...590 B173 ms

Your first network request is the most important. Reduce its latency by avoiding redirects, ensuring a fast server response, and enabling text compression.

Why this matters

Performance issues directly impact user engagement and conversion rates.

These insights are also available in the Chrome DevTools Performance Panel - record a trace to view more detailed information.

The maximum potential First Input Delay that your users could experience is the duration of the longest task. Learn more about the Maximum Potential First Input Delay metric.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Redirects introduce additional delays before the page can be loaded. Learn how to avoid page redirects.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Estimated savings: 806 ms
URLTime Spent
britishmuseum.org/806 ms
www.britishmuseum.org/0.0 ms

Time to Interactive is the amount of time it takes for the page to become fully interactive. Learn more about the Time to Interactive metric.

Why this matters

Performance issues directly impact user engagement and conversion rates.

TTI

Diagnostics

Minifying JavaScript files can reduce payload sizes and script parse time. Learn how to minify JavaScript.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Estimated savings: 320 ms 5.6 KiB
URLTransfer SizeEst Savings
www.britishmuseum.org/core/misc/drupal.js?v=11.3.77.1 KiB5.6 KiB

Reduce unused rules from stylesheets and defer CSS not used for above-the-fold content to decrease bytes consumed by network activity. Learn how to reduce unused CSS.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Estimated savings: 470 ms 39.9 KiB
URLTransfer SizeEst Savings
/sites/default/files/css/css_qv6dCFGN2Vda1nUS7_s-LrSxyqnB...43.8 KiB39.9 KiB

Reduce unused JavaScript and defer loading scripts until they are required to decrease bytes consumed by network activity. Learn how to reduce unused JavaScript.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Estimated savings: 2.7 s 574.4 KiB
URLTransfer SizeEst Savings
/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vH...111.3 KiB75.4 KiB
www.googletagmanager.com/gtm.js?id=GTM-MW5VCK189.5 KiB74.0 KiB
www.googletagmanager.com/gtag/destination?id=G-08TLB9R8X1&cx=c&gtm=4e64h1173.9 KiB66.0 KiB
consent.cookiebot.com/Framework/IAB/consent-sdk-2.3.js87.7 KiB64.2 KiB
www.googletagmanager.com/gtag/js?id=AW-869763654&cx=c&gtm=4e64h1144.2 KiB63.7 KiB
www.googletagmanager.com/gtag/js?id=AW-967338294&cx=c&gtm=4e64h1144.2 KiB63.6 KiB
www.googletagmanager.com/gtag/js?id=AW-944964254&cx=c&gtm=4e64h1144.1 KiB63.1 KiB
www.googletagmanager.com/gtag/js?id=DC-8361401&cx=c&gtm=4e64h1130.0 KiB61.2 KiB
consent.cookiebot.com/uc.js35.5 KiB22.2 KiB
/ec5f4b04-e699-4bea-a9de-eda95d4d9fb7/cc.js?renew=false&r...297.4 KiB21.1 KiB

Consider reducing the time spent parsing, compiling, and executing JS. You may find delivering smaller JS payloads helps with this. Learn how to reduce Javascript execution time.

Why this matters

Performance issues directly impact user engagement and conversion rates.

URLTotal CPU TimeScript EvaluationScript Parse
consent.cookiebot.com/uc.js7.2 s2.7 s18 ms
www.britishmuseum.org/1.1 s54 ms4.5 ms
Unattributable861 ms18 ms0.0 ms
/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vH...684 ms237 ms43 ms
www.googletagmanager.com/gtm.js?id=GTM-MW5VCK635 ms536 ms88 ms
www.googletagmanager.com/gtag/destination?id=G-08TLB9R8X1&cx=c&gtm=4e64h1495 ms423 ms67 ms
www.britishmuseum.org/cdn-cgi/challenge-platform/scripts/jsd/main.js405 ms392 ms4.4 ms
www.googletagmanager.com/gtag/js?id=AW-944964254&cx=c&gtm=4e64h1214 ms159 ms53 ms
/ec5f4b04-e699-4bea-a9de-eda95d4d9fb7/cc.js?renew=false&r...202 ms47 ms154 ms
www.googletagmanager.com/gtag/js?id=AW-869763654&cx=c&gtm=4e64h1187 ms136 ms49 ms
www.googletagmanager.com/gtag/js?id=AW-967338294&cx=c&gtm=4e64h1185 ms138 ms46 ms
www.googletagmanager.com/gtag/js?id=DC-8361401&cx=c&gtm=4e64h1174 ms129 ms44 ms
www.britishmuseum.org/core/assets/vendor/jquery/jquery.min.js?v=4.0.073 ms39 ms23 ms
consent.cookiebot.com/Framework/IAB/consent-sdk-2.3.js62 ms31 ms30 ms

Consider reducing the time spent parsing, compiling and executing JS. You may find delivering smaller JS payloads helps with this. Learn how to minimize main-thread work

Why this matters

Performance issues directly impact user engagement and conversion rates.

CategoryTime Spent
Script Evaluation5.1 s
Parse HTML & CSS4.5 s
Other1.5 s
Style & Layout689 ms
Script Parsing & Compilation630 ms
Rendering136 ms
Garbage Collection128 ms

Large network payloads cost users real money and are highly correlated with long load times. Learn how to reduce payload sizes.

Why this matters

Performance issues directly impact user engagement and conversion rates.

URLTransfer Size
bmwebsitestreaming.blob.core.windows.net/bmvideo/Tour_of_the_British_Museum.mp410.3 MiB
/ec5f4b04-e699-4bea-a9de-eda95d4d9fb7/cc.js?renew=false&r...297.7 KiB
www.googletagmanager.com/gtm.js?id=GTM-MW5VCK189.9 KiB
www.googletagmanager.com/gtag/destination?id=G-08TLB9R8X1&cx=c&gtm=4e64h1174.0 KiB
www.googletagmanager.com/gtag/js?id=AW-967338294&cx=c&gtm=4e64h1144.2 KiB
www.googletagmanager.com/gtag/js?id=AW-869763654&cx=c&gtm=4e64h1144.2 KiB
www.googletagmanager.com/gtag/js?id=AW-944964254&cx=c&gtm=4e64h1144.2 KiB
www.googletagmanager.com/gtag/js?id=DC-8361401&cx=c&gtm=4e64h1130.1 KiB
/sites/default/files/js/js_u3kNJ_Z2LZHlpL78jbhLsQ8GatG5vH...111.8 KiB
/sites/default/files/styles/1_1_media_small/public/2019-1...101.6 KiB

More information about the performance of your application. These numbers don't directly affect the Performance score.

●Layout shift culprits
●Optimize DOM size
●Font display
●LCP breakdown
●Modern HTTP
●Optimize viewport for mobile
●Minify CSS
●User Timing marks and measures 5 user timings
●Avoid long main-thread tasks 20 long tasks found
●Avoid non-composited animations 3 animated elements found
●Image elements have explicit `width` and `height`
●Page didn't prevent back/forward cache restoration
●Network Requests
●Network Round Trip Times 70 ms
●Server Backend Latencies 620 ms
●Tasks
●Diagnostics
●Metrics
●Screenshot Thumbnails
●Final Screenshot
●Script Treemap Data
●Resources Summary
●Initial server response time was short Root document took 20 ms
●Avoid large layout shifts 2 layout shifts found
○INP breakdown
76

Accessibility

These checks highlight opportunities to improve the accessibility of your web app. Automatic detection can only detect a subset of issues and does not guarantee the accessibility of your web app, so manual testing is also encouraged.

ARIA

Some ARIA parent roles must contain specific child roles to perform their intended accessibility functions. Learn more about roles and required children elements.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failing Elements
Consent Details Ad Settings About div.ckb-modal-bgshade > div.ckb-modal > div.ckb-modal__tablist-wrapper > ul.ckb-tablist

Some ARIA child roles must be contained by specific parent roles to properly perform their intended accessibility functions. Learn more about ARIA roles and required parent element.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failing Elements
Consent div.ckb-modal__tablist-wrapper > ul.ckb-tablist > li.ckb-tablist__tab > button#ckb-tab-consent
Details div.ckb-modal__tablist-wrapper > ul.ckb-tablist > li.ckb-tablist__tab > button#ckb-tab-details
Ad Settings div.ckb-modal__tablist-wrapper > ul.ckb-tablist > li.ckb-tablist__tab > button#ckb-tab-adsettings
About div.ckb-modal__tablist-wrapper > ul.ckb-tablist > li.ckb-tablist__tab > button#ckb-tab-about

Assistive technologies, like screen readers, can't interpret ARIA attributes with invalid names. Learn more about valid ARIA attributes.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failing Elements
The British Museum British Museum Consent Details Ad Settings About Responsible… body#page-top > div#cookiebot

ARIA dialog elements without accessible names may prevent screen readers users from discerning the purpose of these elements. Learn how to make ARIA dialog elements more accessible.

Why this matters

Informational: a Permissions-Policy directive showing feature -> allowed origins.

Source: MDN Permissions-Policy

Failing Elements
The British Museum British Museum Consent Details Ad Settings About Responsible… body#page-top > div#cookiebot

These are opportunities to improve the usage of ARIA in your application which may enhance the experience for users of assistive technology, like a screen reader.

Tables and lists

Screen readers have a specific way of announcing lists. Ensuring proper list structure aids screen reader output. Learn more about proper list structure.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failing Elements
Egypt Read more Desire, love and identity Read the blog Animals See the collect… div.teaser-listing__container > div.carousel-container > div.carousel > ul#swiper-wrapper-f854fb6b8d5f61002
Inspired by the Museum https://www.britishmuseumshoponline.org/inspired-by/insp… div.teaser-listing__container > div.carousel-container > div.carousel > ul#swiper-wrapper-2f6981859f8735e2

Screen readers require list items (`<li>`) to be contained within a parent `<ul>`, `<ol>` or `<menu>` to be announced properly. Learn more about proper list structure.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failing Elements
Consent div.ckb-modal > div.ckb-modal__tablist-wrapper > ul.ckb-tablist > li.ckb-tablist__tab
Details div.ckb-modal > div.ckb-modal__tablist-wrapper > ul.ckb-tablist > li.ckb-tablist__tab
Ad Settings div.ckb-modal > div.ckb-modal__tablist-wrapper > ul.ckb-tablist > li.ckb-tablist__tab
About div.ckb-modal > div.ckb-modal__tablist-wrapper > ul.ckb-tablist > li.ckb-tablist__tab

These are opportunities to improve the experience of reading tabular or list data using assistive technology, like a screen reader.

Best practices

Touch targets with sufficient size and spacing help users who may have difficulty targeting small controls to activate the targets. Learn more about touch targets.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failing Elements
Privacy policy nav#block-footerlegallinks > ul.menu > li.menu-item > a.menu__link
Terms of use nav#block-footerlegallinks > ul.menu > li.menu-item > a.menu__link
Chinese site 中文 (Opens in new window) nav#block-footerlegallinks > ul.menu > li.menu-item > a.menu__link

These items highlight common accessibility best practices.

Visible text labels that do not match the accessible name can result in a confusing experience for screen reader users. Learn more about accessible names.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Failing Elements
partners div#ckb-content-consent > div.ckb-modal__text > p > a
○Interactive controls are keyboard focusable
○Interactive elements indicate their purpose and state
○The page has a logical tab order
○Visual order on the page follows DOM order
○User focus is not accidentally trapped in a region
○The user's focus is directed to new content added to the page
○HTML5 landmark elements are used to improve navigation
○Offscreen content is hidden from assistive technology
○Custom controls have associated labels
○Custom controls have ARIA roles
●`[aria-*]` attributes match their roles
●`[aria-hidden="true"]` is not present on the document `<body>`
●`[role]`s have all required `[aria-*]` attributes
●`[role]` values are valid
●`[aria-*]` attributes have valid values
●Buttons have an accessible name
●Image elements have `[alt]` attributes
●Form elements have associated labels
●`[user-scalable="no"]` is not used in the `<meta name="viewport">` element and the `[maximum-scale]` attribute is not less than 5.
●`button`, `link`, and `menuitem` elements have accessible names
●ARIA attributes are used as specified for the element's role
●`[aria-hidden="true"]` elements do not contain focusable descendents
●Elements use only permitted ARIA attributes
●Background and foreground colors have a sufficient contrast ratio
●Document has a `<title>` element
●`<html>` element has a `[lang]` attribute
●`<html>` element has a valid value for its `[lang]` attribute
●Links are distinguishable without relying on color.
●Links have a discernible name
●No element has a `[tabindex]` value greater than 0
●`[lang]` attributes have a valid value
●Heading elements appear in a sequentially-descending order
●Document has a main landmark.
●Deprecated ARIA roles were not used
●`<video>` elements contain a `<track>` element with `[kind="captions"]`
●Uses ARIA roles only on compatible elements
○`[accesskey]` values are unique
○ARIA input fields have accessible names
○ARIA `meter` elements have accessible names
○ARIA `progressbar` elements have accessible names
○Elements with the `role=text` attribute do not have focusable descendents.
○ARIA toggle fields have accessible names
○ARIA `tooltip` elements have accessible names
○ARIA `treeitem` elements have accessible names
○The page contains a heading, skip link, or landmark region
○`<dl>`'s contain only properly-ordered `<dt>` and `<dd>` groups, `<script>`, `<template>` or `<div>` elements.
○Definition list items are wrapped in `<dl>` elements
○ARIA IDs are unique
○No form fields have multiple labels
○`<frame>` or `<iframe>` elements have a title
○`<html>` element has an `[xml:lang]` attribute with the same base language as the `[lang]` attribute.
○Input buttons have discernible text.
○`<input type="image">` elements have `[alt]` text
○The document does not use `<meta http-equiv="refresh">`
○`<object>` elements have alternate text
○Select elements have associated label elements.
○Skip links are focusable.
○Cells in a `<table>` element that use the `[headers]` attribute refer to table cells within the same table.
○`<th>` elements and elements with `[role="columnheader"/"rowheader"]` have data cells they describe.
○Tables have different content in the summary attribute and `<caption>`.
○All heading elements contain content.
○Image elements do not have `[alt]` attributes that are redundant text.
○Identical links have the same purpose.
○Tables use `<caption>` instead of cells with the `[colspan]` attribute to indicate a caption.
○`<td>` elements in a large `<table>` have one or more table headers.
81

Best Practices

General

Deprecated APIs will eventually be removed from the browser. Learn more about deprecated APIs.

Why this matters

Performance issues directly impact user engagement and conversion rates.

Deprecation / WarningSource
SharedStorage
www.britishmuseum.org/cdn-cgi/challenge-platform/scripts/jsd/main.js
StorageType.persistent is deprecated. Please use standardized navigator.storage instead.
www.britishmuseum.org/cdn-cgi/challenge-platform/scripts/jsd/main.js
Fledge
www.britishmuseum.org/cdn-cgi/challenge-platform/scripts/jsd/main.js
●Uses HTTPS
●Avoids third-party cookies
●Allows users to paste into input fields
●Avoids requesting the geolocation permission on page load
●Avoids requesting the notification permission on page load
●Displays images with correct aspect ratio
●Serves images with appropriate resolution
●Page has the HTML doctype
●Properly defines charset
●No browser errors logged to the console
●No issues in the `Issues` panel in Chrome Devtools
●Ensure CSP is effective against XSS attacks
●Use a strong HSTS policy
●Ensure proper origin isolation with COOP
●Mitigate DOM-based XSS with Trusted Types
●Detected JavaScript libraries
●Page has valid source maps
○Redirects HTTP traffic to HTTPS
○Mitigate clickjacking with XFO or CSP
92

SEO

These checks ensure that your page is following basic search engine optimization advice. There are many additional factors Lighthouse does not score here that may affect your search ranking, including performance on Core Web Vitals. Learn more about Google Search Essentials.

Crawling and Indexing

Search engines may use `href` attributes on links to crawl websites. Ensure that the `href` attribute of anchor elements links to an appropriate destination, so more pages of the site can be discovered. Learn how to make links crawlable

Why this matters

Performance issues directly impact user engagement and conversion rates.

Uncrawlable Link
partners div#ckb-content-consent > div.ckb-modal__text > p > a
details section div#ckb-content-consent > div.ckb-modal__text > p > a

To appear in search results, crawlers need access to your app.

○Structured data is valid
●Page isn’t blocked from indexing
●Document has a `<title>` element
●Document has a meta description
●Page has successful HTTP status code
●Links have descriptive text
●robots.txt is valid
●Image elements have `[alt]` attributes
●Document has a valid `hreflang`
●Document has a valid `rel=canonical`

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