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Add footnote about SC 2.4.8, fix gemtext footnotes

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52
content/posts/website-best-practices.gmi
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@ -214,7 +214,7 @@ A supplementary metric to use alongside download size is round trips. Estimate t
Understanding round-trips requires understanding your server's approach to congestion control.
Historically, TCP congestion control approaches typically set an initial window size to ten TCP packets and grew this value with each round-trip. Under most setups, this meant that the first round-trip could include 1460 bytes. The following round-trip could deliver under three kilobytes.⁶
Historically, TCP congestion control approaches typically set an initial window size to ten TCP packets and grew this value with each round-trip. Under most setups, this meant that the first round-trip could include 1460 bytes. The following round-trip could deliver under three kilobytes.⁷
Nowadays, servers typically employ BBR-based congestion control. It allows for regular "spikes" in window size, but the initial window size is still small.
@ -224,7 +224,7 @@ HTTP/3 uses QUIC instead of TCP, which makes things a bit different; the importa
### The golden kilobyte
Assume that your first impression must fit in the first kilobyte. Make good use of this golden kilobyte; most or all of it will likely be taken up by HTTP headers.⁸ Ideally, the first kilobyte transferred should inform the client of all blocking resources required, possibly using preload directives; all of these resources can then begin downloading over the same multiplexed HTTP/2 connection before the current round-trip finishes! Note that this works best if you took my earlier advice to avoid third-party content.
Assume that your first impression must fit in the first kilobyte. Make good use of this golden kilobyte; most or all of it will likely be taken up by HTTP headers.⁹ Ideally, the first kilobyte transferred should inform the client of all blocking resources required, possibly using preload directives; all of these resources can then begin downloading over the same multiplexed HTTP/2 connection before the current round-trip finishes! Note that this works best if you took my earlier advice to avoid third-party content.
Apply these strategies in moderation. Including extra preload directives in your document markup might not help as much as you think, since their impact on page size could negate minor improvements. Micro-optimizations have diminishing returns; past a certain point, your effort is better spent elsewhere.
@ -430,7 +430,7 @@ Some people raised fingerprinting concerns when I suggested using the default "s
I don't know much about fingerprinting, except that 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.
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 all the available fonts on a user's system, the user's canvas fingerprint, window dimensions, etc. Some of these can be mitigated by Firefox's protections against fingerprinting, but these protections understandably override user font preferences:
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 all the available fonts on a user's system,⁸ the user's canvas fingerprint, window dimensions, etc. Some of these can be mitigated by Firefox's protections against fingerprinting, but these protections understandably override user font preferences:
=> https://support.mozilla.org/en-US/kb/firefox-protection-against-fingerprinting Firefox's protection against fingerprinting
@ -440,7 +440,7 @@ Ultimately, surveillance self-defense on the web is an arms race full of trade-o
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.
In your stylesheets, avoid using "px" where possible. Define sizes and dimensions using relative units (preferably "em"). Exceptions exist for some decorations (e.g. borders), but they are uncommon. Set font size and line-spacing with a percentage and a unitless value, respectively:
In your stylesheets, avoid using "px" where possible. Define sizes and dimensions using relative units (preferably "em"). Exceptions exist for some decorations (e.g. borders),⁵ but they are uncommon. Set font size and line-spacing with a percentage and a unitless value, respectively:
```
font: 107.5%/1.5 sans-serif;
@ -451,7 +451,7 @@ font: 107.5%/1.5 sans-serif;
Expect some readers to have images disabled or unloaded. Examples include:
* Blind readers
* Users with metered connections: sometimes they disable all images, and other times they only disable images surpassing a size threshold⁵
* Users with metered connections: sometimes they disable all images, and other times they only disable images surpassing a size threshol⁶
* People experiencing packet loss who fail to download some images
* Users of textual browsers
@ -529,7 +529,7 @@ A StackOverflow thread about comic transcripts outlines a good approach to seman
=> https://stackoverflow.com/questions/65564539/what-is-the-semantically-correct-way-to-include-transcript-from-a-comic What is the semantically correct way to include transcript from a comic?
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 "aria-describedby" to semantically link the figure and the transcript.⁹
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 "aria-describedby" to semantically link the figure and the transcript.¹⁰
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.
@ -719,7 +719,7 @@ Color schemes should also look good to users who apply gamma adjustments. Most o
Some typographers insist that underlined on-screen text is obsolete and hyperlinks are no exception.
=> https://practicaltypography.com/underlining.html Underlining | Butterick’s Practical Typography¹⁰
=> https://practicaltypography.com/underlining.html Underlining | Butterick’s Practical Typography¹¹
I disagree. One reason is that underlines make it easy to separate multiple consecutive inline links:
@ -749,7 +749,7 @@ Lossless or lossy JPEG compression. Note that JPEG is an inherently lossy format
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.
=> https://github.com/AOMediaCodec/libavif avifenc (lossless or lossy), included in libavif
The reference AVIF encoder, included in libavif.¹¹ 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.
The reference AVIF encoder, included in libavif.¹² 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.
I put together a quick script to losslessly optimize images using these programs in my dotfile repo:
@ -997,7 +997,7 @@ Soft hyphens are great for splitting up text, but some text should stay together
10&nbsp;cm
```
Practical Typography by Matthew Butterick,¹⁰ a typographer, describes where to use the non-breaking space in more detail:
Practical Typography by Matthew Butterick,¹¹ a typographer, describes where to use the non-breaking space in more detail:
=> https://practicaltypography.com/nonbreaking-spaces.html nonbreaking spaces, Butterick's Practical Typography
@ -1315,7 +1315,7 @@ Screen readers on touch screen devices are also quite different from their deskt
Screen reader implementations often skip punctuation marks like the exclamation point ("!"). Ensure that meaning doesn't rely too heavily on such punctuation.
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.¹⁴
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.¹⁵
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.
@ -1381,7 +1381,7 @@ Your page should easily pass the harshest of tests without any extra effort if i
These tests begin reasonably, but gradually grow absurd. Once again, use your judgement.
1. Test in all three major browser engines: Blink, Gecko, and WebKit.
2. Evaluate the heaviness and complexity of your scripts (if any) by testing with your browser's JIT compilation disabled.¹²
2. Evaluate the heaviness and complexity of your scripts (if any) by testing with your browser's JIT compilation disabled.¹³
3. Test using the Tor Browser's safest security level enabled (disables JS and other features).
4. Load just the HTML. No CSS, no images, etc. Try loading without inline CSS as well for good measure.
5. Print some pages in black-and-white, preferably with a simple laser printer.
@ -1394,7 +1394,7 @@ These tests begin reasonably, but gradually grow absurd. Once again, use your ju
12. Test with unorthodox graphical browser engines, like NetSurf, Dillo, Servo, or the Serenity OS browser.
13. Test how your page renders in ancient browsers, like Netscape Navigator or Tkhtml. Use a TLS terminator or serve over HTTP from localhost.
14. Try printing out your page in black-and-white from an unorthodox graphical browser.
15. Download your webpage and test how multiple word processors render and generate PDFs from it.¹³
15. Download your webpage and test how multiple word processors render and generate PDFs from it.¹⁴
16. Combine conversion tools. Combine an HTML-to-EPUB converter and an EPUB-to-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.
17. Build a time machine. Travel decades--or perhaps centuries--into the future. Keep going forward until the WWW is breathing its last breath. Test your site on future browsers. Figuring out how to transfer your files onto their computers might take some time, but you have a time machine so that shouldn't be too hard. When you finish, go back in time to meet Benjamin Franklin:
@ -1536,32 +1536,38 @@ A special thanks goes out to GothAlice for the questions she answered in #webdev
=> https://en.wikipedia.org/wiki/Progressive_enhancement Progressive Enhancement (Wikipedia)
=> https://whalecoiner.com/articles/progressive-enhancement Yes, progressive enhancement is a fucking moral argument
⁴ Decoration is more than cosmetic. The "Color overrides and accessibility" sub-section describes how some decorations, like borders, improve accessibility.
⁴ Each of these flows can be visually displayed using a breadcrumbs list; doing so can meet a AAA WCAG criterion:
⁵ 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.
=> https://w3c.github.io/wcag/understanding/location.html Success Criterion 2.4.8: "Location"
⁶ If you'd like more details about TCP, here's a great introduction:
I opted to meet the criterion a different way. Since all my pages are linked by my site's global navigation or my "posts" page (also in the global navigation), I just used "aria-current" and made the currently-relevant entry in my global navigation a <strong> element.
⁵ Decoration is more than cosmetic. The "Color overrides and accessibility" sub-section describes how some decorations, like borders, improve accessibility.
⁶ 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.
⁷ If you'd like more details about TCP, here's a great introduction:
=> https://hpbn.co/building-blocks-of-tcp/ High-Performance Browser Networking, by Ilya Grigorik
⁷ 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 of this approach.
⁸ 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 of this approach.
=> https://browserleaks.com/fonts BrowserLeaks font fingerprinting demo. Warning: the page might hog your CPU for a while.
⁸ HPACK and QPACK header compression includes dictionaries containing common headers. If a header matches one of these common values, its effective size can be reduced to a single byte. If a header has an uncommon value, consider minifying it by removing unnecessary whitespace. Remember that if your golden first kilobyte already lists all essential resources, these could be considered premature optimizations. Real bottlenecks lie elsewhere.
⁹ HPACK and QPACK header compression includes dictionaries containing common headers. If a header matches one of these common values, its effective size can be reduced to a single byte. If a header has an uncommon value, consider minifying it by removing unnecessary whitespace. Remember that if your golden first kilobyte already lists all essential resources, these could be considered premature optimizations. Real bottlenecks lie elsewhere.
=> https://datatracker.ietf.org/doc/html/rfc7541#appendix-A RFC 7541: HPACK static table definition
=> https://quicwg.org/base-drafts/draft-ietf-quic-qpack.html#appendix-A QPACK: Header Compression for HTTP/3
⁹ Once it gains basic support across all browsers and screen readers, I might recommend using aria-details instead of aria-describedby for more complex descriptions. Right now, aria-details is only supported by JAWS. WAI-ARIA 1.2 describes aria-details with an example similar to the one I gave for image transcripts.
¹⁰ Once it gains basic support across all browsers and screen readers, I might recommend using aria-details instead of aria-describedby for more complex descriptions. Right now, aria-details is only supported by JAWS. WAI-ARIA 1.2 describes aria-details with an example similar to the one I gave for image transcripts.
=> https://a11ysupport.io/tech/aria/aria-details_attribute Current support for aria-details
=> https://www.w3.org/TR/wai-aria-1.2/#aria-details aria-details specification
¹⁰ Practical Typography 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.
¹¹ Practical Typography 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.
I find Practical Typography 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.
¹¹ 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.
¹² 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.
¹² Consider disabling the JIT for your normal browsing too; doing so removes whole classes of vulnerabilities. In Firefox, toggle javascript.options.ion, javascript.options.baselinejit, javascript.options.native_regexp, javascript.options.asmjs, and javascript.options.wasm in about:config; in Chromium, run chromium with `--js-flags='--jitless'`; in the Tor Browser, set the security level to "Safer".
¹³ Consider disabling the JIT for your normal browsing too; doing so removes whole classes of vulnerabilities. In Firefox, toggle javascript.options.ion, javascript.options.baselinejit, javascript.options.native_regexp, javascript.options.asmjs, and javascript.options.wasm in about:config; in Chromium, run chromium with `--js-flags='--jitless'`; in the Tor Browser, set the security level to "Safer".
¹³ 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.
¹⁴ 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.
Fun fact: Microsoft Outlook renders HTML email with Microsoft Word's proprietary HTML engine.
¹⁴ 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.
¹⁵ 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.

88
content/posts/website-best-practices.md
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@ -192,7 +192,7 @@ More than one way is available to locate a Web page within a set of Web pages ex
{{< /quotecaption >}}
{{</quotation>}}
Here are some example flows that start with loading a homepage:
Here are some example flows that start with loading a homepage:[^4]
* A homepage has a link to a list of pages in a category. Your reader loads the homepage, navigates to the list page, and then navigates to the target page.
@ -200,7 +200,7 @@ Here are some example flows that start with loading a homepage:
* A homepage has a "search" box. The reader searches for the target page and clicks a result on the result page.
Assume one of your readers has caching enabled, but their current cache is empty. They have a link to your homepage. Your reader should be able to perform at least two different flows to reach a target page, starting with navigating to your homepage. The total size transferred across their entire flow is the metric worth optimizing, not the weight of a single page. Set a performance budget for this flow.
Assume one of your readers has caching enabled, but their current cache is empty. They have a link to your homepage. Your reader should be able to perform at least two different flows to reach a target page, starting with navigating to your homepage. The total size transferred across their entire flow is the metric worth optimizing, not the weight of a single page. Set a performance budget for this flow. A "home, posts list, target page" flow can take a user from my homepage to this page using under 150&nbsp;KiB.
Data is a scarce resource on metered connections; don't waste it on unnecessary information. At least half the data transferred across the flow should be semantically-meaningful compressed markup. Try testing a "lite" version of a page with non-semantic markup removed: strip any `<div>` or `<span>` elements, or attributes that don't have semantic value. Compare this "lite" page's compressed markup size with the total download size of an actual page. Do this for every page across a flow.
@ -242,7 +242,7 @@ A supplementary metric to use alongside download size is round trips. Estimate t
Understanding round-trips requires understanding your server's approach to congestion control.
Historically, TCP congestion control approaches typically set an initial window size to ten TCP packets and grew this value with each round-trip. Under most setups, this meant that the first round-trip could include 1460 bytes. The following round-trip could deliver under three kilobytes.[^4]
Historically, TCP congestion control approaches typically set an initial window size to ten TCP packets and grew this value with each round-trip. Under most setups, this meant that the first round-trip could include 1460 bytes. The following round-trip could deliver under three kilobytes.[^5]
Nowadays, servers typically employ BBR-based congestion control. It allows for regular "spikes" in window size, but the initial window size is still small. Find more details in the slides from <span class="h-cite" itemprop="citation" itemscope itemtype="https://schema.org/PresentationDigitalDocument"> <cite class="p-name" itemprop="name headline" ><a class="u-url" itemprop="url" href="https://labs.apnic.net/presentations/store/2019-09-05-bbr.pdf">TCP and BBR</a></cite> (<span itemprop="encodingFormat">application/<wbr>pdf</span>) by {{<indieweb-person first-name="Geoff" last-name="Huston" itemprop="author" url="https://www.potaroo.net/" org="APNiC" org-url="https://www.apnic.net/">}}</span>.
@ -250,7 +250,7 @@ HTTP/3 uses QUIC instead of TCP, which makes things a bit different; the importa
### The golden kilobyte
Assume that your first impression must fit in the first kilobyte. Make good use of this golden kilobyte; most or all of it will likely be taken up by HTTP headers.[^5] Ideally, the first kilobyte transferred should inform the client of all blocking resources required, possibly using preload directives; all of these resources can then begin downloading over the same multiplexed HTTP/2 connection before the current round-trip finishes! Note that this works best if you took [my advice to avoid third-party content](#third-party-content).
Assume that your first impression must fit in the first kilobyte. Make good use of this golden kilobyte; most or all of it will likely be taken up by HTTP headers.[^6] Ideally, the first kilobyte transferred should inform the client of all blocking resources required, possibly using preload directives; all of these resources can then begin downloading over the same multiplexed HTTP/2 connection before the current round-trip finishes! Note that this works best if you took [my advice to avoid third-party content](#third-party-content).
Apply these strategies in moderation. Including extra preload directives in your document markup might not help as much as you think, since their impact on page size could negate minor improvements. Micro-optimizations have diminishing returns; past a certain point, your effort is better spent elsewhere.
@ -351,7 +351,7 @@ Pages should finish making all `GET` network requests while loading. This makes
One example is pagination. It's easier to download one long article ahead of time, but inconvenient to load each page separately. Displaying content all at once also improves searchability. The single-page approach has obvious limits: don't expect users to happily download a single-page novel.
Another common offender is infinite-scrolling. In addition to requiring JavaScript, infinite-scrolling also makes it difficult for readers to find their old place upon re-visiting a page. This creates harsh consequences for accidental navigation. WordPress documentation lists [more problems with infinite scrolling](https://make.wordpress.org/accessibility/handbook/markup/infinite-scroll/).[^6]
Another common offender is infinite-scrolling. In addition to requiring JavaScript, infinite-scrolling also makes it difficult for readers to find their old place upon re-visiting a page. This creates harsh consequences for accidental navigation. WordPress documentation lists [more problems with infinite scrolling](https://make.wordpress.org/accessibility/handbook/markup/infinite-scroll/).[^7]
A hybrid between the two is paginated content in which users click a "load next page" link to insert the next page at the end of the current page (typically using "dynamic content replacement"). It's essentially the same as infinite scrolling, except additional content is loaded after a click rather than by scrolling. This is only slightly less bad than infinite scrolling; it still has the same fundamental issue of allowing readers to lose their place.
@ -440,7 +440,7 @@ Moreover, some search implemen&shy;tations (such as the one built into Firefox)
### Problem&shy;atic overrides {#problematic-overrides}
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.[^7] 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.
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.[^8] 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.
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.
@ -473,7 +473,7 @@ Some people raised fingerprinting concerns when I suggested using the default "s
I don't know much about fingerprinting, except that 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.
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,[^8] 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.
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,[^9] 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.
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.
@ -481,7 +481,7 @@ Ultimately, surveillance self-defense on the web is an arms race full of trade-o
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.
In your stylesheets, avoid using `px` where possible. Define sizes and dimensions using relative units (preferably `em`). Exceptions exist for some decorations[^9] (e.g. borders), but they are uncommon.
In your stylesheets, avoid using `px` where possible. Define sizes and dimensions using relative units (preferably `em`). Exceptions exist for some decorations (e.g. borders),[^10] but they are uncommon.
{{<codefigure>}} {{< codecaption lang="CSS" >}}
@ -501,14 +501,14 @@ Beyond alt-text
Expect some readers to have images disabled or unloaded. Examples include:
* Blind readers
* Users with metered connections: sometimes they disable all images, and other times they only disable images surpassing a size threshold[^10]
* Users with metered connections: sometimes they disable all images, and other times they only disable images surpassing a size threshold[^11]
* People experiencing packet loss who fail to download some images
* Users of textual browsers
Accordingly, follow good practices for alt-text:
* Concisely summarize the image content the best you can, without repeating the surrounding content.
* Images should usually have alt-text under 100 char&shy;acters.[^11] Save longer descriptions for a caption or <code>aria-<wbr>des&shy;cribedby</code>. Exceptions exist.
* Images should usually have alt-text under 100 char&shy;acters.[^12] Save longer descriptions for a caption or <code>aria-<wbr>des&shy;cribedby</code>. Exceptions exist.
* Don't include significant information that isn't present in the image; I'll cover how to handle supple&shy;mentary information in the next subsections.
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.
@ -583,7 +583,7 @@ A <dfn>`longdesc`</dfn> attribute used to be another way to reference an image t
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.
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>des&shy;cribedby</code> to semantically link the figure and the transcript.[^12]
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>des&shy;cribedby</code> to semantically link the figure and the transcript.[^13]
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.
@ -667,7 +667,7 @@ Even if you set custom colors, ensure that the page is compatible with color ove
[This page's canonical location](https://seirdy.one/2020/11/23/website-best-practices.html) 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.
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.[^13]
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.[^14]
<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).
@ -745,14 +745,14 @@ Accounting for halation, overstimulation, and high-contrast needs is hard to do
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". <span itemprop="citation" itemscope itemtype="https://schema.org/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">}}</span>. 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.
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.[^14]
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.[^15]
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.
In defense of link under&shy;lines {#in-defense-of-link-underlines}
----------------------------------
Some typographers insist that [underlined on-screen text is obsolete](https://practicaltypography.com/underlining.html),[^15] and that hyperlinks are no exception. I disagree.
Some typographers insist that [underlined on-screen text is obsolete](https://practicaltypography.com/underlining.html),[^16] and that hyperlinks are no exception. I disagree.
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.
@ -797,7 +797,7 @@ Some image optimization tools I use:
: 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.
`avifenc`
: The reference AVIF encoder, included in [libavif](https://github.com/AOMediaCodec/libavif).[^16] 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.
: The reference AVIF encoder, included in [libavif](https://github.com/AOMediaCodec/libavif).[^17] 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.
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 Web&shy;Assembly-compiled encoders; I've heard good things about it.
@ -918,7 +918,7 @@ Users of <abbr title="assistive technology">AT</abbr>s such as screen readers pr
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.
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.[^17] When it makes sense to do so, place skippable content in its own sections and/or at the end of its parent section.
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.[^18] When it makes sense to do so, place skippable content in its own sections and/or at the end of its parent section.
### Arbitrary viewports
@ -1006,7 +1006,7 @@ Where long inline `<code>` elements can trigger horizontal scrolling, consider a
### Keeping text together
Soft hyphens are great for splitting up text, but some text should stay together. The phrase "10&nbsp;cm", for instance, would flow poorly if "10" and "cm" appeared on separate lines. Splitting text becomes especially painful on narrow viewports. A non-breaking space keeps the surrounding text from being re-flowed. Use the `&nbsp;` HTML entity instead of a space: `10&nbsp;cm`. <span itemprop="mentions" itemscope itemtype="https://schema.org/Book">{{<cited-work name="Practical Typography" url="https://practicaltypography.com/">}} by {{<indieweb-person first-name="Matthew" last-name="Butterick" url="https://mbtype.com/bio.html">}},[^15] a typographer,</span> describes [where to use the non-breaking space](https://briefs.video/videos/is-progressive-enhancement-dead-yet/) in more detail.
Soft hyphens are great for splitting up text, but some text should stay together. The phrase "10&nbsp;cm", for instance, would flow poorly if "10" and "cm" appeared on separate lines. Splitting text becomes especially painful on narrow viewports. A non-breaking space keeps the surrounding text from being re-flowed. Use the `&nbsp;` HTML entity instead of a space: `10&nbsp;cm`. <span itemprop="mentions" itemscope itemtype="https://schema.org/Book">{{<cited-work name="Practical Typography" url="https://practicaltypography.com/">}} by {{<indieweb-person first-name="Matthew" last-name="Butterick" url="https://mbtype.com/bio.html">}},[^16] a typographer,</span> describes [where to use the non-breaking space](https://briefs.video/videos/is-progressive-enhancement-dead-yet/) in more detail.
One exception to the rules from <cite>Practical Typography</cite>: don't use a non-breaking space if it would trigger two-dimensional scrolling on a narrow viewport. Between broken text and two-dimensional scrolling, broken text is the lesser evil. I personally set a cutoff at 2.5&nbsp;cm (1&nbsp;inch) at 125% zoom.
@ -1232,7 +1232,7 @@ On one hand, users who need enhanced focus visibility may override the default f
The WCAG [Success Criterion 2.4.12](https://w3c.github.io/wcag/guidelines/22/#focus-appearance-enhanced) recommends making focus indicators 2&nbsp;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.
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.[^18]
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.[^19]
{{<codefigure>}}
@ -1310,7 +1310,7 @@ Screen readers on touch screen devices are also quite different from their deskt
Screen reader implemen&shy;tations often skip punctuation marks like the exclamation point ("!"). Ensure that meaning doesn't rely too heavily on such punctuation.
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.[^19]
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.[^20]
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.
@ -1339,7 +1339,7 @@ No matter how simple a page is, I don't think simplicity eliminates the need for
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.
These are the tools I use regularly. I've deliberately excluded tools that would be redundant.[^20]
These are the tools I use regularly. I've deliberately excluded tools that would be redundant.[^21]
1. [Nu HTML checker](https://validator.nu/): The W3C's official HTML validator. Valid HTML ensures broader compatibility with a wider range of agents. Note that it uses Jigsaw under the hood for CSS validation, which hasn't implemented support for certain CSS features I've reco&shy;mmended elsewhere on this page. Watch out for false positives.
@ -1347,7 +1347,7 @@ These are the tools I use regularly. I've deliberately excluded tools that would
3. [Light&shy;house](https://developers.google.com/web/tools/lighthouse/): An auditing tool by Google that uses the DevTools protocol in any Chromium-based browser. Skip the "Access&shy;ibility" 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.
4. [Webhint](https://webhint.io/): Similar to Light&shy;house. 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 agg&shy;ressively[^21].
4. [Webhint](https://webhint.io/): Similar to Light&shy;house. 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 agg&shy;ressively[^22].
5. [IBM Equal Access Access&shy;ibility Checker](https://www.ibm.com/able/toolkit/verify/automated/): Has a scope similar to axe-core. Its "Sensory Characteristics" audit seems unique.
@ -1371,7 +1371,7 @@ These tests begin reasonably, but gradually grow absurd. Once again, use your ju
1. Test in all three major browser engines: Blink, Gecko, and WebKit.
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.[^22]
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.[^23]
3. Test using the Tor Browser's safest security level enabled (disables JS and other features).
@ -1397,7 +1397,7 @@ These tests begin reasonably, but gradually grow absurd. Once again, use your ju
14. Try printing out your page in black-and-white from an unorthodox graphical browser.
15. Download your webpage and test how multiple word processors render and generate PDFs from it.[^23]
15. Download your webpage and test how multiple word processors render and generate PDFs from it.[^24]
16. 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.
@ -1548,49 +1548,51 @@ A special thanks goes out to GothAlice for the questions she answered in <samp>#
[^3]: Here's an [overview of PE](https://en.wikipedia.org/wiki/Progressive_enhancement) and [my favorite write-up on the subject](https://whalecoiner.com/articles/progressive-enhancement).
[^4]: <span itemprop="citation" itemscope itemtype="https://schema.org/TechArticle">{{<cited-work name="High-Performance Browser Networking" url="https://hpbn.co/building-blocks-of-tcp/" extraName="headline">}} by {{<indieweb-person first-name="Ilya" last-name="Grigorik" url="https://www.igvita.com/" itemprop="author">}}</span> gives a great introduction to how TCP works, if you'd like more details.
[^4]: Each of these flows can be visually displayed using a breadcrumbs list; doing so can meet the WCAG [Success Criterion 2.4.8: Location](https://w3c.github.io/wcag/understanding/location.html). I opted to meet the criterion a different way. Since all my pages are linked by my site's global navigation or my "posts" page (also in the global navigation), I just used `aria-current` and made the currently-relevant entry in my global navigation a `<strong>` element.
[^5]: HPACK and QPACK header compression includes dictionaries containing common header names, and some common header values; HPACK lists them in "Appendix A" of <span itemprop="citation" itemscope itemtype="https://schema.org/TechArticle">{{<cited-work name="RFC 7541" extraName="headline" url="https://datatracker.ietf.org/doc/html/rfc7541#appendix-A">}}</span>. If a header name or name-value pair one of these predefined table entries, its effective size can be reduced to a single byte. If a header has a value that isn't covered by the table, consider minifying it by removing unnecessary whitespace.
[^5]: <span itemprop="citation" itemscope itemtype="https://schema.org/TechArticle">{{<cited-work name="High-Performance Browser Networking" url="https://hpbn.co/building-blocks-of-tcp/" extraName="headline">}} by {{<indieweb-person first-name="Ilya" last-name="Grigorik" url="https://www.igvita.com/" itemprop="author">}}</span> gives a great introduction to how TCP works, if you'd like more details.
[^6]: HPACK and QPACK header compression includes dictionaries containing common header names, and some common header values; HPACK lists them in "Appendix A" of <span itemprop="citation" itemscope itemtype="https://schema.org/TechArticle">{{<cited-work name="RFC 7541" extraName="headline" url="https://datatracker.ietf.org/doc/html/rfc7541#appendix-A">}}</span>. If a header name or name-value pair one of these predefined table entries, its effective size can be reduced to a single byte. If a header has a value that isn't covered by the table, consider minifying it by removing unnecessary whitespace.
Remember that if your golden first kilobyte already lists all essential resources, these could be considered premature optimi&shy;zations. Real bottlenecks lie elsewhere.
[^6]: Ironically, that page doesn't load the main text without JavaScript despite citing a JavaScript requirement as a downside. If you can't load the page, the same issues with infinte scroll are outlined in the "Accessibility concerns for infinite scroll" section of <span itemprop="citation" itemscope itemtype="https://schema.org/BlogPosting">{{<cited-work url="https://addyosmani.com/blog/infinite-scroll-without-layout-shifts/" name="Infinite Scroll without Layout Shifts" extraName="headline">}} by {{<indieweb-person itemprop="author" first-name="Addy" last-name="Osmani" url="https://addyosmani.com/">}}</span>.
[^7]: Ironically, that page doesn't load the main text without JavaScript despite citing a JavaScript requirement as a downside. If you can't load the page, the same issues with infinte scroll are outlined in the "Accessibility concerns for infinite scroll" section of <span itemprop="citation" itemscope itemtype="https://schema.org/BlogPosting">{{<cited-work url="https://addyosmani.com/blog/infinite-scroll-without-layout-shifts/" name="Infinite Scroll without Layout Shifts" extraName="headline">}} by {{<indieweb-person itemprop="author" first-name="Addy" last-name="Osmani" url="https://addyosmani.com/">}}</span>.
[^7]: 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.
[^8]: 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.
[^8]: 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. [Browser&shy;Leaks has a demo](https://browserleaks.com/fonts) of this approach. Warning: the page might hog your CPU for a while.
[^9]: 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. [Browser&shy;Leaks has a demo](https://browserleaks.com/fonts) of this approach. Warning: the page might hog your CPU for a while.
[^9]: Decoration is more than cosmetic. The [color overrides and accessibility](#color-overrides-and-accessibility) sub-section describes how some decorations, like borders, improve access&shy;ibility.
[^10]: Decoration is more than cosmetic. The [color overrides and accessibility](#color-overrides-and-accessibility) sub-section describes how some decorations, like borders, improve access&shy;ibility.
[^10]: 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.
[^11]: 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.
[^11]: [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.
[^12]: [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.
[^12]: Once it gains basic support across all browsers and screen readers, I might recommend using `aria-details` instead of <code>aria-<wbr>des&shy;cribedby</code> for more complex descriptions. Right now, [`aria-details` is only supported by JAWS](https://a11ysupport.io/tech/aria/aria-details_attribute). <span itemprop="mentions" itemscope itemtype="https://schema.org/TechArticle">{{<cited-work name="WAI-ARIA 1.2" url="https://www.w3.org/TR/wai-aria-1.2/#aria-details">}}</span> describes `aria-details` with an example similar to the one I gave in [code snippet 5](#xkcd-html).
[^13]: Once it gains basic support across all browsers and screen readers, I might recommend using `aria-details` instead of <code>aria-<wbr>des&shy;cribedby</code> for more complex descriptions. Right now, [`aria-details` is only supported by JAWS](https://a11ysupport.io/tech/aria/aria-details_attribute). <span itemprop="mentions" itemscope itemtype="https://schema.org/TechArticle">{{<cited-work name="WAI-ARIA 1.2" url="https://www.w3.org/TR/wai-aria-1.2/#aria-details">}}</span> describes `aria-details` with an example similar to the one I gave in [code snippet 5](#xkcd-html).
[^13]: Since <abbr title="Windows High Contrast Mode">WHCM</abbr> sets colors indepen&shy;dently of explicitly-defined ARIA roles, it's a good way to test adherence to [the First Rule of ARIA](#first-rule-of-aria).
[^14]: Since <abbr title="Windows High Contrast Mode">WHCM</abbr> sets colors indepen&shy;dently of explicitly-defined ARIA roles, it's a good way to test adherence to [the First Rule of ARIA](#first-rule-of-aria).
[^14]: 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 compromise.
[^15]: 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 compromise.
[^15]: <span itemprop="mentions" itemscope itemtype="https://schema.org/Book">{{<cited-work name="Practical Typography" url="https://practicaltypography.com/">}}</span> only renders invisible text without JavaScript. You can use a textual browser, screen reader, copy-paste the page contents elsewhere, use a reader-mode implemen&shy;tation, 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.
[^16]: <span itemprop="mentions" itemscope itemtype="https://schema.org/Book">{{<cited-work name="Practical Typography" url="https://practicaltypography.com/">}}</span> only renders invisible text without JavaScript. You can use a textual browser, screen reader, copy-paste the page contents elsewhere, use a reader-mode implemen&shy;tation, 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.
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.
[^16]: 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 accu&shy;rately.
[^17]: 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 accu&shy;rately.
[^17]: 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.
[^18]: 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.
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.
[^18]: If you'd like to learn more, <span itemprop="mentions" itemscope itemtype="https://schema.org/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">}}</span> has far more details on making accessible focus indicators.
[^19]: If you'd like to learn more, <span itemprop="mentions" itemscope itemtype="https://schema.org/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">}}</span> has far more details on making accessible focus indicators.
[^19]: 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.
[^20]: 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.
[^20]: I excluded PageSpeed Insights and GTMetrix since those are mostly covered by Lighthouse. I excluded Security Headers, since its approach seems to be recommen&shy;ding headers regardless of whether or not they are necessary. It penalizes forgoing the <code>Per&shy;missions-<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>Per&shy;missions-<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).
[^21]: I excluded PageSpeed Insights and GTMetrix since those are mostly covered by Lighthouse. I excluded Security Headers, since its approach seems to be recommen&shy;ding headers regardless of whether or not they are necessary. It penalizes forgoing the <code>Per&shy;missions-<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>Per&shy;missions-<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).
[^21]: My site caches HTML documents for ten minutes and caches the RSS feed for several hours. I disagree with webhint's recommen&shy;dations 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` recommen&shy;dations: 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.
[^22]: My site caches HTML documents for ten minutes and caches the RSS feed for several hours. I disagree with webhint's recommen&shy;dations 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` recommen&shy;dations: 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.
[^22]: Consider disabling the JIT for your normal browsing too; doing so removes whole classes of vulnera&shy;bilities. In Firefox, navigate to <samp>about:<wbr>config</samp> and toggle some flags under <code>javascript<wbr>.options</code>.
[^23]: Consider disabling the JIT for your normal browsing too; doing so removes whole classes of vulnera&shy;bilities. In Firefox, navigate to <samp>about:<wbr>config</samp> and toggle some flags under <code>javascript<wbr>.options</code>.
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@ -1606,7 +1608,7 @@ A special thanks goes out to GothAlice for the questions she answered in <samp>#
In Chromium and derivatives, run the browser with `--js-flags='--jitless'`; in the Tor Browser, set the security level to "Safer".
[^23]: 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.
[^24]: 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.
Fun fact: Microsoft Outlook renders HTML email with Microsoft Word's proprietary HTML engine.