firefox/testing/web-platform/tests/css/css-highlight-api/highlight-priority.html

<!DOCTYPE html>
<html>
<head>
    <title>Highlight priority attribute is mutable</title>
    <link rel="help" href="https://drafts.csswg.org/css-highlight-api-1/#priorities">
    <script src="/resources/testharness.js"></script>
    <script src="/resources/testharnessreport.js"></script>
    <style>
        ::highlight(yellow-highlight) {
            background-color: yellow;
        }
        ::highlight(green-highlight) {
            background-color: green;
        }
        ::highlight(blue-highlight) {
            background-color: blue;
        }
    </style>
</head>
<body>
    <span id="green-highlight">Green</span>
    <span id="yellow-highlight">Yellow</span>
    <span id="blue-highlight">Blue</span>
    <span id="yellow-blue-highlight">Yellow-Blue</span>

    <script>
    test(() => {
        let yellowBlue = document.getElementById("yellow-blue-highlight");

        let green = document.getElementById("green-highlight");
        let highlightGreen = new Highlight(new StaticRange({
            startContainer: green.childNodes[0],
            startOffset: 0,
            endContainer: green.childNodes[0],
            endOffset: 6
        }));

        let yellow = document.getElementById("yellow-highlight");
        let highlightYellow = new Highlight(new StaticRange({
            startContainer: yellow.childNodes[0],
            startOffset: 0,
            endContainer: yellow.childNodes[0],
            endOffset: 6
        }), new StaticRange({
            startContainer: yellowBlue.childNodes[0],
            startOffset: 0,
            endContainer: yellowBlue.childNodes[0],
            endOffset: 6
        }));

        let blue = document.getElementById("blue-highlight");
        let highlightBlue = new Highlight(new StaticRange({
            startContainer: blue.childNodes[0],
            startOffset: 0,
            endContainer: blue.childNodes[0],
            endOffset: 4
        }), new StaticRange({
            startContainer: yellowBlue.childNodes[0],
            startOffset: 0,
            endContainer: yellowBlue.childNodes[0],
            endOffset: 11
        }));

        CSS.highlights.set("yellow-highlight", highlightYellow);
        CSS.highlights.set("green-highlight", highlightGreen);
        CSS.highlights.set("blue-highlight", highlightBlue);

        highlightYellow.priority = 10;
        highlightBlue.priority = -1;

        assert_equals(highlightYellow.priority, 10);
        assert_equals(highlightGreen.priority, 0);
        assert_equals(highlightBlue.priority, -1);
    });
    </script>
</body>
</html>