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1.4.1 Use of Color Understanding doc: add note concerning same color case #3286

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Aug 30, 2023
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1.4.1 Use of Color Understanding doc: add note concerning same color case #3286

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1.4.1 Use of Color Understanding doc: add note concerning same color …
scottaohara Jul 17, 2023
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reword first sentence
scottaohara Jul 18, 2023
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scottaohara Jul 19, 2023
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scottaohara Aug 25, 2023
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scottaohara Aug 29, 2023
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further updates to note text
scottaohara Aug 29, 2023
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scottaohara Aug 29, 2023
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alastc Aug 29, 2023
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mbgower Aug 29, 2023
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Merge branch 'main' into patch-3
alastc Aug 30, 2023
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50 changes: 30 additions & 20 deletions understanding/20/use-of-color.html
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Original file line number Diff line number Diff line change
@@ -1,9 +1,9 @@
<!DOCTYPE html>
<html lang="en" xml:lang="en" xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta charset="UTF-8"></meta>
<meta charset="UTF-8" />
<title>Understanding Use of Color</title>
<link rel="stylesheet" type="text/css" href="../../css/sources.css" class="remove"></link>
<link rel="stylesheet" type="text/css" href="../../css/sources.css" class="remove" />
</head>
<body>
<h1>Understanding Use of Color</h1>
Expand Down Expand Up @@ -63,6 +63,16 @@ <h2>Intent of Use of Color</h2>

</div>

<div class="note">

<p>This criterion does not apply to situations where color has <em>not</em> been used to convey information, indicate an action,
prompt a response or distinguish a visual element. For instance, a hyperlink which has been styled to appear no different than neighboring
static text would not fail this success criterion, as there would be no color differentiation between the actionable hyperlink text
and the adjacent static text. Such styling would result for poor usability for many users, regardless of disability.
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</p>

</div>

<div class="note">

<p>This criterion does not directly address the needs of users with assistive technologies.
Expand All @@ -83,24 +93,24 @@ <h2>Intent of Use of Color</h2>
</div>

<div class="note">

<p>Most user agents provide users with a color-only cue that a link has been previously activated by them ("visited"). However, several technical constraints result in authors having very limited control over these color-only indications of visited links. The technical constraints are as follows:
<ol>
<li>
User agents constrain the exposure of a link's visited state due to <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/Privacy_and_the_:visited_selector">privacy concerns</a>. Author queries to user agents will indicate all links have not been visited.
</li>
<li>
Any available information on the visited state of a link would be inaccurate since it is both user and browser-dependent. Even if an author could accurately get information on previously activated links by a certain user, the author would be constrained to the current browser's preserved history, and would be unable to determine if the user had visited the page using a different browser (or if the history was not preserved, either from cache clearing or use of private sessions).
</li>
<li>
Authors can <em>only</em> use color to modify the <code>:visited</code> CSS pseudoclass style. The technology constrains any non-color styling. Due to palette limitations, an author cannot use color alone to achieve 3:1 contrast between link and non-link text as well as between visited and unvisited links while also achieving 4.5:1 contrast for all link and non-link text.
</li>
<li>
Authors also cannot set the visited state of links. The anchor element does not include a "visited" attribute; therefore the author has no ability to alter the state through an attribute setting. As such, authors cannot achieve <a href="info-and-relationships">1.3.1 Info and Relationships</a> or
<a href="name-role-value">4.1.2 Name, Role, Value</a> in regard to visited links.
</li>
</ol>
</p>
<p>Most user agents provide users with a color-only cue that a link has been previously activated by them ("visited"). However, several technical constraints result in authors having very limited control over these color-only indications of visited links. The technical constraints are as follows</p>

<ol>
<li>
User agents constrain the exposure of a link's visited state due to <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/Privacy_and_the_:visited_selector">privacy concerns</a>. Author queries to user agents will indicate all links have not been visited.
</li>
<li>
Any available information on the visited state of a link would be inaccurate since it is both user and browser-dependent. Even if an author could accurately get information on previously activated links by a certain user, the author would be constrained to the current browser's preserved history, and would be unable to determine if the user had visited the page using a different browser (or if the history was not preserved, either from cache clearing or use of private sessions).
</li>
<li>
Authors can <em>only</em> use color to modify the <code>:visited</code> CSS pseudoclass style. The technology constrains any non-color styling. Due to palette limitations, an author cannot use color alone to achieve 3:1 contrast between link and non-link text as well as between visited and unvisited links while also achieving 4.5:1 contrast for all link and non-link text.
</li>
<li>
Authors also cannot set the visited state of links. The anchor element does not include a "visited" attribute; therefore the author has no ability to alter the state through an attribute setting. As such, authors cannot achieve <a href="info-and-relationships">1.3.1 Info and Relationships</a> or
<a href="name-role-value">4.1.2 Name, Role, Value</a> in regard to visited links.
</li>
</ol>

<p>For these reasons, setting or conveying a link's visited status is not an author responsibility. Where color alone distinguishes between visited and unvisited links, it does not result in a failure of this Success Criterion, even where the contrast between the two link colors is below 3:1. Note that authors must continue to ensure that all text links meet contrast minimums against the page background (SC 1.4.3).</p>
</div>
Expand Down