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@ -423,7 +423,7 @@ Long pages with many DOM nodes may benefit from CSS containment, a more recently
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{{< /quotecaption >}}
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{{</quotation>}}
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Leveraging containment and `content-visibility` is a progressive enhancement, so there aren't any serious implications for older browsers. I use `content-visibility` to defer rendering off-screen entries in my archives. Doing so allows me to serve long archive pages instead of resorting to pagination, with page-length limited only by download size.
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Leveraging containment and `content-visibility` is a progressive enhancement, so there aren't any serious implications for older browsers. I use `content-visibility` to defer rendering off-screen entries in my archives. Doing so allows me to serve long archive pages instead of resorting to pagination, with page-length limited only by download size. In my tests using Lighthouse with Chromium Devtools' simulated CPU throttling,[^11] this article rendered faster _with_ containment-enabled CSS than without any custom stylesheets at all.
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Using containment for content at the end of the page is relatively safe. Using it for content earlier in the page risks introducing [layout shifts](#layout-shifts). Eliminate the layout shifts by calculating a value for the `contain-intrinsic-size` property. {{<mention-work itemtype="TechArticle">}}{{<cited-work url="https://www.terluinwebdesign.nl/en/css/calculating-contain-intrinsic-size-for-content-visibility/" name="Calculating 'contain-intrinsic-size' for 'content-visibility'" extraName="headline">}}, by {{<indieweb-person first-name="Thijs" last-name="Terluin" url="https://www.terluinwebdesign.nl/en/about-us/thijs-terluin/" org="Teluin Webdesign" org-url="https://www.terluinwebdesign.nl/en/" itemprop="author">}}{{</mention-work>}}, is a comprehensive guide to calculating intrinsic size values.
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@ -471,7 +471,7 @@ Moreover, some search implementations (such as the one built into Firefox) suppo
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### Problematic overrides {#problematic-overrides}
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Search is so essential to some users' ability to navigate that some desktop users enable "type-ahead" search, to automatically begin a search upon typing multiple characters.[^11] If you ignored my advice to avoid JavaScript, at least think twice before using it to define custom keyboard shortcuts which interfere with this type of functionality. I singled out type-ahead search, but there are countless other examples of uncommon keyboard behavior that JavaScript overrides interfere with.
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Search is so essential to some users' ability to navigate that some desktop users enable "type-ahead" search, to automatically begin a search upon typing multiple characters.[^12] If you ignored my advice to avoid JavaScript, at least think twice before using it to define custom keyboard shortcuts which interfere with this type of functionality. I singled out type-ahead search, but there are countless other examples of uncommon keyboard behavior that JavaScript overrides interfere with.
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Another problematic override is scroll-behavior. Enforcing smooth-scrolling (e.g., with the `scroll-behavior` CSS property) can interfere with the use of in-page search by slowing down jumps between matches. Rapidly darting around the page with smooth scrolling can cause motion sickness. Simply relying on users to override default behaviors violates the "inclusive by default" directive I encourage, since user preferences are fingerprintable and shift responsibility away from developers.
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@ -506,7 +506,7 @@ Some people raised fingerprinting concerns when I suggested using the default "s
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You can't do font enumeration or accurately calculate font metrics without JavaScript. Since text-based websites that follow these best-practices don't send requests after the page loads and have no scripts, they shouldn't be able to fingerprint via font identification.
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Other websites can still fingerprint via font enumeration using JavaScript. They don't need to stop at seeing what sans-serif maps to: they can see available fonts on a user's system,[^12] the user's canvas fingerprint, window dimensions, etc. Some of these can be mitigated by [Firefox's protections against fingerprinting](https://support.mozilla.org/en-US/kb/firefox-protection-against-fingerprinting), but these protections understandably override user font preferences.
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Other websites can still fingerprint via font enumeration using JavaScript. They don't need to stop at seeing what sans-serif maps to: they can see available fonts on a user's system,[^13] the user's canvas fingerprint, window dimensions, etc. Some of these can be mitigated by [Firefox's protections against fingerprinting](https://support.mozilla.org/en-US/kb/firefox-protection-against-fingerprinting), but these protections understandably override user font preferences.
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Ultimately, surveillance self-defense on the web is an arms race full of trade-offs. If you want both privacy and customizability, the web is not the place to look; try Gemini or Gopher instead.
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@ -514,7 +514,7 @@ Ultimately, surveillance self-defense on the web is an arms race full of trade-o
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Browsers allow users to zoom by adjusting size metrics. Additionally, most browsers allow users to specify a minimum font size. Minimum sizes don't always work; setting size values in `px` can override these settings.
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In your stylesheets, avoid using `px` where possible. Define sizes and dimensions using relative units (preferably `em`). Exceptions exist for rare items that that shouldn't scale with zoom (e.g. decoration, minimum margins).[^13]
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In your stylesheets, avoid using `px` where possible. Define sizes and dimensions using relative units (preferably `em`). Exceptions exist for rare items that that shouldn't scale with zoom (e.g. decoration, minimum margins).[^14]
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{{<codefigure>}} {{< codecaption lang="CSS" >}}
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@ -535,7 +535,7 @@ Expect some readers to have images disabled or unloaded. Examples include:
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* Blind readers.
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* Users with metered connections: sometimes they disable all images, and other times they only disable images surpassing a size.[^14]
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* Users with metered connections: sometimes they disable all images, and other times they only disable images surpassing a size.[^15]
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* People experiencing packet loss who fail to download some images.
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@ -545,13 +545,13 @@ Accordingly, follow good practices for alt-text:
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* Concisely summarize the image content the best you can, without repeating the surrounding content.
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* Images should usually have alt-text under 100 ch.[^15] Save longer descriptions for a caption or <code>aria-<wbr />describedby</code>. Exceptions exist; this is just a weak norm.
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* Images should usually have alt-text under 100 ch.[^16] Save longer descriptions for a caption or <code>aria-<wbr />describedby</code>. Exceptions exist; this is just a weak norm.
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* Don't include significant information that isn't present in the image; I'll cover how to handle supplementary information in the next subsections.
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The <abbr title="Web Accessibility Initiative">WAI</abbr> provides some guidelines in <cite>[An `alt` Decision Tree](https://www.w3.org/WAI/tutorials/images/decision-tree/)</cite>. It's a little lacking in nuance, but makes for a good starting point. Remember that guidelines and "good practices" always have exceptions.
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Alt text isn't just for blind readers; sighted readers who can't load an image will see alt-text in its place. This alt text might be confined to the image container, so small images should have shorter alt text.[^16]
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Alt text isn't just for blind readers; sighted readers who can't load an image will see alt-text in its place. This alt text might be confined to the image container, so small images should have shorter alt text.[^17]
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### Putting images in context
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@ -621,7 +621,7 @@ A <dfn>`longdesc`</dfn> attribute used to be another way to reference an image t
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The recommended way to link to a transcript is by hyperlinking the image (i.e., wrapping it with `<a>`) or semantically grouping the image with its transcript. Put a short summary in the alt-text, and mention the availability of a transcript in a visible caption.
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A [StackOverflow thread about comic transcripts](https://stackoverflow.com/questions/65564539/what-is-the-semantically-correct-way-to-include-transcript-from-a-comic) outlines a good approach to semantically grouping images and transcripts, and my approach is similar. I group an image, alt-text, and caption in a `<figure>` element and follow it with a transcript in a `<details>` element. I use <code>aria-<wbr />describedby</code> to semantically link the figure and the transcript.[^17]
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A [StackOverflow thread about comic transcripts](https://stackoverflow.com/questions/65564539/what-is-the-semantically-correct-way-to-include-transcript-from-a-comic) outlines a good approach to semantically grouping images and transcripts, and my approach is similar. I group an image, alt-text, and caption in a `<figure>` element and follow it with a transcript in a `<details>` element. I use <code>aria-<wbr />describedby</code> to semantically link the figure and the transcript.[^18]
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An image, alt-text, figure caption, and transcript combine to form a complex relationship that should be grouped together in a single landmark. I put all three inside a `<section>` with a heading, and give the group an `aria-label` that indicates the presence of the three sub-elements. Using a `section` landmark ensures that the figure and caption remain together as a single unit. The [html code](#xkcd-html) for the [xkcd comic earlier in the page](#infinite-scrolling) is a representative example.
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@ -705,7 +705,7 @@ Even if you set custom colors, ensure that the page is compatible with color ove
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[This page's canonical location](https://seirdy.one/posts/2020/11/23/website-best-practices/) is an example application of Technique C25 (and the related [Technique G148](https://www.w3.org/WAI/WCAG22/Techniques/general/G148)). It only uses non-default colors when a user agent requests a dark color scheme (using the `prefers-color-scheme` CSS media query; see the next subsection) and for lightening borders. Any image with a solid background may match the page background; to ensure that their dimensions are clear, I surrounded them with borders. Most browsers will render these borders with the default foreground color, which should be visually distinct from the background. I included borders and/or horizontal rules to break up some sections, since heading-based delineation is either unavailable or insufficient for them. When overriding color schemes, the page layout remains clear.
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Color overrides go well beyond simple foreground and background color changes. Windows High Contrast Mode (<abbr title="Windows High Contrast Mode">WHCM</abbr>) is perhaps the best example. [WHCM makes advanced modifications to color palettes](#win-hcm): it colors elements with a user-specified palette, all according to semantic markup while ignoring ARIA overrides.[^18]
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Color overrides go well beyond simple foreground and background color changes. Windows High Contrast Mode (<abbr title="Windows High Contrast Mode">WHCM</abbr>) is perhaps the best example. [WHCM makes advanced modifications to color palettes](#win-hcm): it colors elements with a user-specified palette, all according to semantic markup while ignoring ARIA overrides.[^19]
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<abbr title="Windows High Contrast Mode">WHCM</abbr> leads the standardization process for the `forced-colors` CSS media feature, but it isn't the only implementation of the underlying idea. If you navigate to <samp>about:preferences</samp> in Firefox and activate the <samp translate="yes">Colors</samp> button in the "Language and Appearance" section, you'll be presented with the option to override website palettes with [your own default colors](#default-colors).
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@ -761,7 +761,7 @@ This image is an approximation of what halation looks like, cropped from <a href
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If you can't bear the thought of parting with your solid-black background, worry not: there exists a CSS media feature and client-hint for contrast preferences called `prefers-contrast`. It takes the parameters `no-preference`, `less`, and `more`. You can serve increased-contrast pages to those who request `more`, and vice versa. Check section 11.3 of the W3C {{<mention-work itemtype="TechArticle">}}{{<cited-work url="https://drafts.csswg.org/mediaqueries-5/#prefers-contrast" name="Media Queries Level 5" extraName="headline">}}{{</mention-work>}} specification for more information.
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I personally like a foreground and background of `#E9E9E9` and `#191919`, respectively. These shades seem to be as far apart as possible without causing accessibility issues: `#191919` is barely bright enough to create a soft "glow" capable of minimizing halos among slightly astigmatic users, but won't ruin contrast on cheap displays. I also support a `prefers-contrast: less` media query which lightens the background to `#333`.[^19]
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I personally like a foreground and background of `#E9E9E9` and `#191919`, respectively. These shades seem to be as far apart as possible without causing accessibility issues: `#191919` is barely bright enough to create a soft "glow" capable of minimizing halos among slightly astigmatic users, but won't ruin contrast on cheap displays. I also support a `prefers-contrast: less` media query which lightens the background to `#333`.[^20]
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### Contrast is complex
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@ -789,7 +789,7 @@ Accounting for halation, overstimulation, and high-contrast needs is hard to do
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Color palettes need to be effective for different types of vision deficiencies (e.g. color blindnesses) and screens. Color blindness is a far more nuanced topic than "the inability to see some colors". {{<mention-work itemprop="citation" itemtype="BlogPosting">}}{{<indieweb-person itemprop="author" first-name="Rob" last-name="Pike" url="http://herpolhode.com/rob/">}} describes his experience in {{<cited-work name="Color blindness" extraName="headline" url="https://commandcenter.blogspot.com/2020/09/color-blindness-is-inaccurate-term.html">}}{{</mention-work>}}. Color blindness manifests in complex ways. Testing in grayscale is a great start, but it doesn't account for all kinds of color vision deficiencies.
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Different screens and display-calibrations render color differently; what may look like a light-gray on a cheap monitor could look nearly black on a high-end OLED screen. Try to test on both high- and low-end displays, especially when designing a dark color scheme.[^20]
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Different screens and display-calibrations render color differently; what may look like a light-gray on a cheap monitor could look nearly black on a high-end OLED screen. Try to test on both high- and low-end displays, especially when designing a dark color scheme.[^21]
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Color schemes should also look good to users who apply gamma adjustments. Most operating systems and desktop environments bundle a feature to reduce the screen color temperature at night, while some individuals may select a higher one in the morning.
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@ -811,7 +811,7 @@ A basic WCAG Level A requirement is for information to not be conveyed solely th
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### In defense of link underlines
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Some typographers insist that [underlined on-screen text is obsolete](https://practicaltypography.com/underlining.html),[^21] and that hyperlinks are no exception. I disagree.
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Some typographers insist that [underlined on-screen text is obsolete](https://practicaltypography.com/underlining.html),[^22] and that hyperlinks are no exception. I disagree.
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Readers already expect underlined text to signify a hyperlink. Don't break fundamental affordances for aesthetics. Underlines are also necessary to distinguish the beginnings and ends of multiple consecutive links, especially among color-blind users.
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@ -889,9 +889,9 @@ Someone using the GitHub issues interface for the first time will struggle to id
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### Against focusable containers
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Screen readers like iOS VoiceOver[^22] fail to follow in-page links whose targets are not focusable. Designers often work around this by annotating link targets with the `tabindex="-1"` HTML attribute. This is a good idea when a link target is a heading or piece of [phrasing content](https://html.spec.whatwg.org/dev/dom.html#phrasing-content). Unfortunately, making large containers focusable ruins keyboard-navigability.
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Screen readers like iOS VoiceOver[^23] fail to follow in-page links whose targets are not focusable. Designers often work around this by annotating link targets with the `tabindex="-1"` HTML attribute. This is a good idea when a link target is a heading or piece of [phrasing content](https://html.spec.whatwg.org/dev/dom.html#phrasing-content). Unfortunately, making large containers focusable ruins keyboard-navigability.
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Normally, if you select some text in a page and press <kbd>Tab</kbd>, the tab-focusable element _after_ the selected text will receive focus. However, if the selectable text is inside a focusable container---even a container with a negative `tabindex`---pressing <kbd>Tab</kbd> will move focus to the _start_ of the container. If you're reading this on a desktop browser, you can experience this first-hand: select some text in this paragraph and press <kbd>Tab</kbd>. Then, do the same in [this snapshot of an excellent _Smashing Magazine_ article](https://web.archive.org/web/20220808163715/https://www.smashingmagazine.com/2022/06/voice-control-usability-considerations-partially-visually-hidden-link-names/).[^23]
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Normally, if you select some text in a page and press <kbd>Tab</kbd>, the tab-focusable element _after_ the selected text will receive focus. However, if the selectable text is inside a focusable container---even a container with a negative `tabindex`---pressing <kbd>Tab</kbd> will move focus to the _start_ of the container. If you're reading this on a desktop browser, you can experience this first-hand: select some text in this paragraph and press <kbd>Tab</kbd>. Then, do the same in [this snapshot of an excellent _Smashing Magazine_ article](https://web.archive.org/web/20220808163715/https://www.smashingmagazine.com/2022/06/voice-control-usability-considerations-partially-visually-hidden-link-names/).[^24]
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{{<image-figure id="focus-container">}} {{<picture name="focus-container" alt="Two screenshots of an article byline above a title. First, the title has selected text; then, the byline is focused.">}}
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@ -923,7 +923,7 @@ Some image optimization tools I use:
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: The reference WebP encoder; has dedicated lossless and lossy modes. Lossy WebP compression isn't always better than JPEG, but lossless WebP consistently beats PNG.
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`avifenc`
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: The reference AVIF encoder, included in [libavif](https://github.com/AOMediaCodec/libavif).[^24] AVIF lossless compression is typically useless, but its lossy compression is pretty unique in that it leans towards detail removal rather than introducing compression artifacts. Note that AVIF is not supported by Safari or most WebKit-based browsers. It also seems unsupported in Microsoft Edge.[^25]
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: The reference AVIF encoder, included in [libavif](https://github.com/AOMediaCodec/libavif).[^25] AVIF lossless compression is typically useless, but its lossy compression is pretty unique in that it leans towards detail removal rather than introducing compression artifacts. Note that AVIF is not supported by Safari or most WebKit-based browsers. It also seems unsupported in Microsoft Edge.[^26]
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I put together [a quick script](https://git.sr.ht/~seirdy/dotfiles/tree/3b722a843f3945a1bdf98672e09786f0213ec6f6/Executables/shell-scripts/bin/optimize-image) to losslessly optimize images using these programs. For lossy compression, I typically use [GNU Parallel](https://www.gnu.org/software/parallel/) to mass-generate images using different options before selecting the smallest image at the minimum acceptable quality. Users who'd rather avoid the command line while performing lossy compression can instead check out [Squoosh](https://squoosh.app/), a JavaScript app that bundles Web­Assembly-compiled encoders; I've heard good things about it.
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@ -1041,7 +1041,7 @@ The first or second heading in the DOM, and the highest heading level, should be
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Remember that not all landmarks are announced by screen readers; for instance, many screen readers don't announce the ending of a `<header>` element in an article. An `<hr>` element is a good way to force the ending of a landmark to be visible: it introduces a thematic break between sections that is visible to assistive technologies and user-agents that don't support CSS.
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Consider adding a "skip link" if some pages require many <kbd>Tab</kbd> keystrokes to reach the main content.[^26] Visually-impaired users generally prefer navigating by headings or landmarks, but screen reader beginners and motor-impaired users still benefit from a skip link. Skip links are especially helpful when pure heading- and landmark-based navigation isn't optimal.
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Consider adding a "skip link" if some pages require many <kbd>Tab</kbd> keystrokes to reach the main content.[^27] Visually-impaired users generally prefer navigating by headings or landmarks, but screen reader beginners and motor-impaired users still benefit from a skip link. Skip links are especially helpful when pure heading- and landmark-based navigation isn't optimal.
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If your skip link toggles visibility states when focused, ensure that it doesn't move any existing content; see [the "Layout shifts" section](#layout-shifts) for more details. If it appears over existing content, it needs to have a solid background; if you set the background color, set a foreground color too as described in [the "About custom colors" section](#about-custom-colors).
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@ -1051,7 +1051,7 @@ Users of <abbr title="assistive technology">AT</abbr>s such as screen readers pr
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Try using a tool to view a list of all your link names. Just about every screen reader and some browser extensions should offer this functionality. Minimize links with ambiguous names, and ensure that identical link names have identical destinations.
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Think twice before placing important content immediately after skippable content such as nested landmarks, long code snippets, figures, and large lists. AT users who wish to skip content may jump directly to the next heading, glossing over anything between the skippable content and subsequent heading; this is especially common on mobile devices.[^27] When it makes sense to do so, place skippable content in its own sections and/or at the end of its parent section.
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Think twice before placing important content immediately after skippable content such as nested landmarks, long code snippets, figures, and large lists. AT users who wish to skip content may jump directly to the next heading, glossing over anything between the skippable content and subsequent heading; this is especially common on mobile devices.[^28] When it makes sense to do so, place skippable content in its own sections and/or at the end of its parent section.
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### Single-column layout
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@ -1140,7 +1140,7 @@ Users employing machine translation will not benefit from your soft hyphens, so
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Where long inline `<code>` elements can trigger horizontal scrolling, consider a scrollable `<pre>` element instead. Making a single element horizontally scrollable is far better than making the entire page scrollable in two dimensions. Hard-wrap code blocks so that they won't horizontally scroll in most widescreen desktop browsers.
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Be sure to test your hyphens with NVDA or Windows Narrator: these screen readers' pronunciation of words can be disrupted by poorly-placed hyphens. Balancing the need to adapt to narrow screens against the need to sound correctly to a screen reader is a complex matter.[^28] The best place to insert a hyphen is between compound words. For example, splitting "Firefighter" into "Fire-fighter" is quite safe. Beyond that, try listening to hyphenated words in NVDA to ensure they remain clear.
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Be sure to test your hyphens with NVDA or Windows Narrator: these screen readers' pronunciation of words can be disrupted by poorly-placed hyphens. Balancing the need to adapt to narrow screens against the need to sound correctly to a screen reader is a complex matter.[^29] The best place to insert a hyphen is between compound words. For example, splitting "Firefighter" into "Fire-fighter" is quite safe. Beyond that, try listening to hyphenated words in NVDA to ensure they remain clear.
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### Keeping text together
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@ -1400,7 +1400,7 @@ On one hand, users who need enhanced focus visibility may override the default f
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The WCAG [Success Criterion 2.4.12](https://w3c.github.io/wcag/guidelines/22/#focus-appearance-enhanced) recommends making focus indicators 2 px thick. While this success criterion is only AAA-level, it's easy enough to meet and beneficial enough to others that we should all meet it.
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You can use `:focus` and `:focus-visible` to highlight selected and keyboard-focused elements, respectively. Take care to only alter styling, not behavior: only keyboard-focusable elements should receive outlines. Modern browser stylesheets use `:focus-visible` instead of `:focus`; old browsers only support `:focus` and re-style a subset of focusable elements. Your stylesheets should do the same, to match browser behavior.[^29]
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You can use `:focus` and `:focus-visible` to highlight selected and keyboard-focused elements, respectively. Take care to only alter styling, not behavior: only keyboard-focusable elements should receive outlines. Modern browser stylesheets use `:focus-visible` instead of `:focus`; old browsers only support `:focus` and re-style a subset of focusable elements. Your stylesheets should do the same, to match browser behavior.[^30]
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{{<codefigure>}}
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@ -1480,7 +1480,7 @@ Screen readers on touch screen devices are also quite different from their deskt
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Screen reader implementations often skip punctuation marks like the exclamation point ("!"). Ensure that meaning doesn't rely too heavily on such punctuation.
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Screen readers have varying levels of verbosity. The default verbosity level doesn't always convey inline emphasis, such as `<em>`, `<code>`, or `<strong>`. Ensure that your meaning carries through without these semantics.[^30]
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Screen readers have varying levels of verbosity. The default verbosity level doesn't always convey inline emphasis, such as `<em>`, `<code>`, or `<strong>`. Ensure that your meaning carries through without these semantics.[^31]
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Default verbosity does, however, convey symbols and emoji. Use symbols and emoji judiciously, since they can get pretty noisy if you aren't careful. Use `aria-labelledby` on symbols when appropriate; I used labels to mark my footnote backlinks, which would otherwise be read as <samp>right arrow curving left</samp>. If you have to use a symbol or emoji, first test how assistive technologies announce it; the emoji name may not communicate what you expect.
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@ -1509,7 +1509,7 @@ No matter how simple a page is, I don't think simplicity eliminates the need for
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Automated tests---especially accessibility tests---are a supplement to manual tests, not a replacement for them. Think of them as time-savers that bring up issues for further research, containing both false positives and false negatives.
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These are the tools I use regularly. I've deliberately excluded tools that would be redundant.[^31]
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These are the tools I use regularly. I've deliberately excluded tools that would be redundant.[^32]
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[Nu HTML checker](https://validator.nu/)
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@ -1518,11 +1518,11 @@ These are the tools I use regularly. I've deliberately excluded tools that would
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[axe-core](https://github.com/dequelabs/axe-core)
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: The current standard in accessibility testing. Most website auditors that run accessibility checks use this library under the hood.
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[Lighthouse](https://developers.google.com/web/tools/lighthouse/)
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: An auditing tool by Google that uses the DevTools protocol in any Chromium-based browser. Skip the "Access­ibility" category, since it just runs a subset of axe-core's audits. The most useful audit is the tap target size check in its "SEO" category. Note that your `sandbox` CSP directive will need to include `allow-scripts` for it to function.
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[<span id="lighthouse">Lighthouse</span>](https://developers.google.com/web/tools/lighthouse/)
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: An auditing tool by Google that uses the DevTools protocol in any Chromium-based browser. Skip the "Access­ibility" category, since it just runs a subset of axe-core's audits. The most useful audit is the tap target size check in its "SEO" category. It's also convenient for measuring performance with CPU throttling, to simulate low-end mobile devices. Note that your `sandbox` CSP directive will need to include `allow-scripts` for it to function.
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[Webhint](https://webhint.io/)
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: Similar to Lighthouse. Again, you can ignore the accessibility audits if you already use axe-core. I personally disagree with some of its hints: the "unneeded HTTP headers" hint ignores the fact that the CSP can have an effect on non-hypertext assets, the "HTTP cache" hint has an unreasonable bias against caching HTML, and the "Correct `Content-Type` header" recommends charset attributes a bit too agg­ressively.[^32]
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: Similar to Lighthouse. Again, you can ignore the accessibility audits if you already use axe-core. I personally disagree with some of its hints: the "unneeded HTTP headers" hint ignores the fact that the CSP can have an effect on non-hypertext assets, the "HTTP cache" hint has an unreasonable bias against caching HTML, and the "Correct `Content-Type` header" recommends charset attributes a bit too agg­ressively.[^33]
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[IBM Equal Access Accessibility Checker](https://www.ibm.com/able/toolkit/verify/automated/)
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: Has a scope similar to axe-core. Its "Sensory Characteristics" audit seems unique.
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@ -1552,7 +1552,7 @@ These tests begin reasonably, but gradually grow absurd. Once again, use your ju
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1. Test in all three major browser engines: Blink, Gecko, and WebKit.
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2. Evaluate the heaviness and complexity of your scripts (if any) by testing with your browser's <abbr title="just-in-time">JIT</abbr> compilation disabled.[^33]
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2. Evaluate the heaviness and complexity of your scripts (if any) by testing with your browser's <abbr title="just-in-time">JIT</abbr> compilation disabled.[^34]
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3. Test using the Tor Browser's safest security level enabled (disables JS and other features).
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@ -1580,7 +1580,7 @@ These tests begin reasonably, but gradually grow absurd. Once again, use your ju
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15. Try printing out your page in black-and-white from an unorthodox graphical browser.
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16. Download your webpage and test how multiple word processors render and generate PDFs from it.[^34]
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16. Download your webpage and test how multiple word processors render and generate PDFs from it.[^35]
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17. Combine conversion tools. Combine an HTML-<wbr />to-<wbr />EPUB converter and an EPUB-<wbr />to-<wbr />PDF converter, or stack multiple article-extraction utilities. Be creative and enjoy breaking your site. When something breaks, examine the breakage and see if it's caused by an issue in your markup, or a CSS feature with an equivalent alternative.
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@ -1764,55 +1764,57 @@ A special thanks goes out to GothAlice for the questions she answered in <samp>#
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[^10]: The benefits of containment are especially noticeable when injecting styles into a page. "Dark mode" and "userstyle" extensions perform noticeably better when enough elements receive layout and paint containment. Containment allows browsers to handle changes to an element independently of the rest of the DOM.
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[^11]: Firefox users [can enable "find as you type"](https://website-archive.mozilla.org/www.mozilla.org/access/access/type-ahead/) by toggling a preference in <samp>about:<wbr />config</samp>. Chromium (and derivatives) users can [install an extension](https://github.com/Foxy/chrome-type-ahead); note that it requires full-page access and performs script injection to work.
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[^11]: [See the "Lighthouse" entry in the "Automated tests" section](#lighthouse). Lighthouse benchmarks my machine with a score of around 1320; with that score, it recommends [throttling my machine by just under 3.1x](https://github.com/patrickhulce/lighthouse-cpu-throttling-calculator/blob/a9c67dc1c58c972a0673bef05756290105334af1/pages/index.js#L11) to simulate a target mobile device. The Chromium team came up with the throttling formula under idealized conditions (the phone isn't overheating, battery-saver mode is off, etc); I go further and throttle between 12x and 13x, still shooting for a perfect performance score. This article is the largest page on my site; it often gets a perfect performance score (100) with my stylesheet enabled, but never reaches 100 when I disable CSS containment or remove my stylesheet.
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[^12]: Iterating through a list of font names to see if each one is available on a user's system is a slow but effective way to determine installed fonts without being granted permission to use the Font Access API. [Browser­Leaks has a demo](https://browserleaks.com/fonts) of this approach. Warning: the page might hog your CPU for a while.
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[^12]: Firefox users [can enable "find as you type"](https://website-archive.mozilla.org/www.mozilla.org/access/access/type-ahead/) by toggling a preference in <samp>about:<wbr />config</samp>. Chromium (and derivatives) users can [install an extension](https://github.com/Foxy/chrome-type-ahead); note that it requires full-page access and performs script injection to work.
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[^13]: Decoration is more than cosmetic. The [color overrides and accessibility](#color-overrides-and-accessibility) sub-section describes how some decorations, like borders, improve access­ibility.
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[^13]: Iterating through a list of font names to see if each one is available on a user's system is a slow but effective way to determine installed fonts without being granted permission to use the Font Access API. [Browser­Leaks has a demo](https://browserleaks.com/fonts) of this approach. Warning: the page might hog your CPU for a while.
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[^14]: uBlock Origin is a popular browser extension for content filtering; it's the most popular Firefox add-on. It includes a built-in feature to block all media elements exceeding a user-configurable size threshold.
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[^14]: Decoration is more than cosmetic. The [color overrides and accessibility](#color-overrides-and-accessibility) sub-section describes how some decorations, like borders, improve access­ibility.
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[^15]: [WebAIM](https://wave.webaim.org/api/docs?format=html) and the [University of Illinois](https://fae.disability.illinois.edu/rulesets/IMAGE_4_EN/) recommend 100 characters; [Tangaru](https://www.tanaguru.com/en/) recommends an even smaller limit of 80 characters. I sometimes exceed 100 characters for detailed images but usually stay below 80.
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[^15]: uBlock Origin is a popular browser extension for content filtering; it's the most popular Firefox add-on. It includes a built-in feature to block all media elements exceeding a user-configurable size threshold.
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[^16]: Browser support for displaying alt-text in place of broken images seems good. More information about support for alt-text exposure can be found on {{<mention-work itemtype="BlogPosting">}}{{<cited-work name="Alternative Text for CSS Generated Content" extraName="headline" url="https://adrianroselli.com/2020/10/alternative-text-for-css-generated-content.html">}}{{</mention-work>}}. That post seems to indicate that Firefox 81 on macOS 10.15 didn't display alt-text, but [users report correct alt-text display](https://cybre.space/@nleigh/108688070682694730) in more recent Firefox versions.
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[^16]: [WebAIM](https://wave.webaim.org/api/docs?format=html) and the [University of Illinois](https://fae.disability.illinois.edu/rulesets/IMAGE_4_EN/) recommend 100 characters; [Tangaru](https://www.tanaguru.com/en/) recommends an even smaller limit of 80 characters. I sometimes exceed 100 characters for detailed images but usually stay below 80.
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[^17]: Once it gains basic support across all browsers and screen readers, I might recommend using `aria-details` instead of <code>aria-<wbr />describedby</code> for more complex descriptions. At the time of writing, [`aria-details` is only supported by JAWS](https://a11ysupport.io/tech/aria/aria-details_attribute). {{<mention-work itemtype="TechArticle">}}{{<cited-work name="WAI-ARIA 1.2" url="https://www.w3.org/TR/wai-aria-1.2/#aria-details">}}{{</mention-work>}} describes `aria-details` with an example similar to the one I gave in [code snippet 5](#xkcd-html).
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[^17]: Browser support for displaying alt-text in place of broken images seems good. More information about support for alt-text exposure can be found on {{<mention-work itemtype="BlogPosting">}}{{<cited-work name="Alternative Text for CSS Generated Content" extraName="headline" url="https://adrianroselli.com/2020/10/alternative-text-for-css-generated-content.html">}}{{</mention-work>}}. That post seems to indicate that Firefox 81 on macOS 10.15 didn't display alt-text, but [users report correct alt-text display](https://cybre.space/@nleigh/108688070682694730) in more recent Firefox versions.
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[^18]: Since <abbr title="Windows High Contrast Mode">WHCM</abbr> sets colors independently of explicitly-defined ARIA roles, it's a good way to test adherence to [the First Rule of ARIA](#first-rule-of-aria).
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[^18]: Once it gains basic support across all browsers and screen readers, I might recommend using `aria-details` instead of <code>aria-<wbr />describedby</code> for more complex descriptions. At the time of writing, [`aria-details` is only supported by JAWS](https://a11ysupport.io/tech/aria/aria-details_attribute). {{<mention-work itemtype="TechArticle">}}{{<cited-work name="WAI-ARIA 1.2" url="https://www.w3.org/TR/wai-aria-1.2/#aria-details">}}{{</mention-work>}} describes `aria-details` with an example similar to the one I gave in [code snippet 5](#xkcd-html).
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[^19]: An earlier version of this article recommended a background of `#111`, but two helpful readers sensitive to overstimulation and halation found `#191919` preferable.
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[^19]: Since <abbr title="Windows High Contrast Mode">WHCM</abbr> sets colors independently of explicitly-defined ARIA roles, it's a good way to test adherence to [the First Rule of ARIA](#first-rule-of-aria).
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[^20]: When making an earlier version of this site's dark-mode color palette, I made the mistake of exclusively testing in cheap or poorly-calibrated displays with bright black points. I mistakenly thought that my `#0b0b0b` background was bright enough to [prevent halation](#halation). Only after testing on a better screen did I realize that it would look almost completely black; I subsequently lightened the background to `#111` to strike a good balance.
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[^20]: An earlier version of this article recommended a background of `#111`, but two helpful readers sensitive to overstimulation and halation found `#191919` preferable.
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[^21]: {{<mention-work itemtype="Book">}}{{<cited-work name="Practical Typography" url="https://practicaltypography.com/">}}{{</mention-work>}} only renders invisible text without JavaScript. You can use a textual browser, screen reader, copy-paste the page contents elsewhere, use a reader-mode implementation, or "view source" to read it without enabling scripts. All of these options will ironically override the carefully-crafted typography of this website about typography.
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[^21]: When making an earlier version of this site's dark-mode color palette, I made the mistake of exclusively testing in cheap or poorly-calibrated displays with bright black points. I mistakenly thought that my `#0b0b0b` background was bright enough to [prevent halation](#halation). Only after testing on a better screen did I realize that it would look almost completely black; I subsequently lightened the background to `#111` to strike a good balance.
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[^22]: {{<mention-work itemtype="Book">}}{{<cited-work name="Practical Typography" url="https://practicaltypography.com/">}}{{</mention-work>}} only renders invisible text without JavaScript. You can use a textual browser, screen reader, copy-paste the page contents elsewhere, use a reader-mode implementation, or "view source" to read it without enabling scripts. All of these options will ironically override the carefully-crafted typography of this website about typography.
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I find <cite>Practical Typography</cite> quite useful for printed works, and incorporated a more moderate version of its advice on soft-hyphens into this page. With a few such exceptions, I generally find it to be poor advice for Web content.
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[^22]: I can't confirm if this is also an issue on VoiceOver for macOS, because I haven't borrowed the hardware required to test it.
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[^23]: I can't confirm if this is also an issue on VoiceOver for macOS, because I haven't borrowed the hardware required to test it.
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[^23]: I linked to a snapshot from the Wayback Machine in hopes that the live version of the Smashing Magazine site will get fixed.
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[^24]: I linked to a snapshot from the Wayback Machine in hopes that the live version of the Smashing Magazine site will get fixed.
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[^24]: libavif links against libaom, librav1e, and/or libsvtav1 to perform AVIF encoding and decoding. libaom is best for this use-case, particularly since libaom can link against libjxl to use its Butteraugli distortion metric. This lets libaom optimize the perceptual quality of lossy encodes much more accurately.
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[^25]: libavif links against libaom, librav1e, and/or libsvtav1 to perform AVIF encoding and decoding. libaom is best for this use-case, particularly since libaom can link against libjxl to use its Butteraugli distortion metric. This lets libaom optimize the perceptual quality of lossy encodes much more accurately.
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[^25]: I find it quite odd that Microsoft Edge doesn't support AVIF. Chromium has supported AVIF for a long time, and Edge is based on Chromium. AVIF is a royalty-free format; I don't know why Microsoft would remove support for it, especially since Microsoft allows adding AVIF support to Windows. I think Edge also removed Chromium's experimental, off-by-default support for JPEG-XL.
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[^26]: I find it quite odd that Microsoft Edge doesn't support AVIF. Chromium has supported AVIF for a long time, and Edge is based on Chromium. AVIF is a royalty-free format; I don't know why Microsoft would remove support for it, especially since Microsoft allows adding AVIF support to Windows. I think Edge also removed Chromium's experimental, off-by-default support for JPEG-XL.
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[^26]: I say that a skip link is useful to reduce the amount of <kbd>Tab</kbd> keystrokes required, but I don't know a good "threshold number" to signify "too many keystrokes". If it takes ten keystrokes to reach the main content, it's probably time to add a skip-link.
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[^27]: I say that a skip link is useful to reduce the amount of <kbd>Tab</kbd> keystrokes required, but I don't know a good "threshold number" to signify "too many keystrokes". If it takes ten keystrokes to reach the main content, it's probably time to add a skip-link.
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[^27]: ATs typically let users navigate by headings, landmarks, paragraphs, and links. Most users prefer skipping article content with heading-based navigation. Keyboard users can bind different keys to different modes of navigation, but mobile users can only access one navigation mode at a time.
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[^28]: ATs typically let users navigate by headings, landmarks, paragraphs, and links. Most users prefer skipping article content with heading-based navigation. Keyboard users can bind different keys to different modes of navigation, but mobile users can only access one navigation mode at a time.
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Mobile users wishing to temporarily switch modes have to stop, change their navigation mode, perform a navigation gesture, and switch back. Mobile users trying to skim an article don't always find this worth the effort and sometimes stick to heading-based navigation even when a different mode would be optimal.
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[^28]: At least, it will be until [NVDA bug 9343](https://github.com/nvaccess/nvda/issues/9343) gets resolved.
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[^29]: At least, it will be until [NVDA bug 9343](https://github.com/nvaccess/nvda/issues/9343) gets resolved.
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[^29]: If you'd like to learn more, {{<mention-work itemtype="BlogPosting">}}{{< cited-work name="A guide to designing accessible, WCAG-compliant focus indicators" url="https://www.sarasoueidan.com/blog/focus-indicators/" extraName="headline" >}} by {{< indieweb-person url="https://www.sarasoueidan.com/" first-name="Sara" last-name="Soueidan" url="https://www.sarasoueidan.com/" itemprop="author">}}{{</mention-work>}} has far more details on making accessible focus indicators.
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[^30]: If you'd like to learn more, {{<mention-work itemtype="BlogPosting">}}{{< cited-work name="A guide to designing accessible, WCAG-compliant focus indicators" url="https://www.sarasoueidan.com/blog/focus-indicators/" extraName="headline" >}} by {{< indieweb-person url="https://www.sarasoueidan.com/" first-name="Sara" last-name="Soueidan" url="https://www.sarasoueidan.com/" itemprop="author">}}{{</mention-work>}} has far more details on making accessible focus indicators.
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[^30]: Screen readers aren't alone here. Several programs strip inline formatting: certain feed readers, search result snippets, and textual browsers invoked with the `-dump` flag are some examples I use every day.
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[^31]: Screen readers aren't alone here. Several programs strip inline formatting: certain feed readers, search result snippets, and textual browsers invoked with the `-dump` flag are some examples I use every day.
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[^31]: I excluded PageSpeed Insights and GTMetrix since those are mostly covered by Lighthouse. I excluded Security Headers, since its approach seems to be recommending headers regardless of whether or not they are necessary. It penalizes forgoing the <code>Permissions-<wbr />Policy</code> header even if the CSP blocks script loading and execution; see [Security Headers issue #103](https://github.com/securityheaders/securityheaders-bugs/issues/103). I personally find the <code>Permissions-<wbr />Policy</code> header quite problematic, as I noted in August 2021 on [webappsec-permissions-policy issue #189](https://github.com/w3c/webappsec-permissions-policy/issues/189#issuecomment-904783021).
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[^32]: I excluded PageSpeed Insights and GTMetrix since those are mostly covered by Lighthouse. I excluded Security Headers, since its approach seems to be recommending headers regardless of whether or not they are necessary. It penalizes forgoing the <code>Permissions-<wbr />Policy</code> header even if the CSP blocks script loading and execution; see [Security Headers issue #103](https://github.com/securityheaders/securityheaders-bugs/issues/103). I personally find the <code>Permissions-<wbr />Policy</code> header quite problematic, as I noted in August 2021 on [webappsec-permissions-policy issue #189](https://github.com/w3c/webappsec-permissions-policy/issues/189#issuecomment-904783021).
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[^32]: My site caches HTML documents for ten minutes and caches the RSS feed for several hours. I disagree with webhint's recommendations against this: cache durations should be based on request rates and how often a resource is updated. I also disagree with some of its `content-type` recommendations: you don't need to declare UTF-8 charsets for SVG content-type headers if the SVG is ASCII-only and called from a UTF-8 HTML document. You gain nothing but header bloat by doing so.
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[^33]: My site caches HTML documents for ten minutes and caches the RSS feed for several hours. I disagree with webhint's recommendations against this: cache durations should be based on request rates and how often a resource is updated. I also disagree with some of its `content-type` recommendations: you don't need to declare UTF-8 charsets for SVG content-type headers if the SVG is ASCII-only and called from a UTF-8 HTML document. You gain nothing but header bloat by doing so.
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[^33]: Consider disabling the JIT for your normal browsing too; doing so removes whole classes of vulnerabilities. In Firefox, navigate to <samp>about:<wbr />config</samp> and toggle some flags under <code>javascript<wbr />.options</code>.
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[^34]: Consider disabling the JIT for your normal browsing too; doing so removes whole classes of vulnerabilities. In Firefox, navigate to <samp>about:<wbr />config</samp> and toggle some flags under <code>javascript<wbr />.options</code>.
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<figure itemprop="hasPart" itemscope="" itemtype="https://schema.org/SoftwareSourceCode">
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<figcaption>
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@ -1828,6 +1830,6 @@ A special thanks goes out to GothAlice for the questions she answered in <samp>#
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In Chromium and derivatives, run the browser with `--js-flags='--jitless'`; in the Tor Browser, set the security level to "Safer".
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[^34]: LibreOffice can also render HTML but has extremely limited support for CSS. OnlyOffice seems to work best, but doesn't load images. If your page is CSS-optional, it should look fine in both.
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[^35]: LibreOffice can also render HTML but has extremely limited support for CSS. OnlyOffice seems to work best, but doesn't load images. If your page is CSS-optional, it should look fine in both.
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