link-rel-attribute-ascii-case-insensitive.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>link element rel is ASCII case-insensitive</title>
<link rel="help" href="https://html.spec.whatwg.org/#the-link-element">
<link rel="help" href="https://html.spec.whatwg.org/#attr-link-rel">
<link rel="help" href="https://html.spec.whatwg.org/#linkTypes">
<meta name="assert" content="link element's rel attribute is ASCII case-insensitive.">
<link rel="mismatch" href="link-rel-attribute-ascii-case-insensitive-notref.html">

<!-- Load sheet with a red background (rel attribute value is case-sensitive
     equal to "stylesheet") -->
<link rel="stylesheet" href="stylesheet.css">

<!-- Load sheet with white background (rel attribute value is ASCII
     case-insensitive equal to "stylesheet") -->
<link rel="StyLeShEeT" href="style.css">

<!-- Do not load sheet with a red background (rel attribute value is
     case-insensitive equal to "stylesheet") -->
<link rel="ſtyleſheet" href="stylesheet.css">

<p>Test passes if background is not red.</p>

chromium/third_party/blink/web_tests/external/wpt/html/semantics/document-metadata/the-link-element/link-rel-attribute-ascii-case-insensitive.html