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chromium/third_party/blink/web_tests/accessibility/aria-describedby-on-input.html 

<html>
<script>
    if (window.testRunner)
        testRunner.dumpAsText();
</script>
<body>
    <span id="message">This computer will self-destruct in</span>
    <input id="time" type="text" value="10" aria-describedby="description"/>
    <span id="unit"> minutes.</span>
    <div id="description">Allows you to specify the number of minutes after which the computer will self-destruct.</div>
    <div id="result"></div>
    
    <script>
        if (window.accessibilityController) {
            var labeledItem = document.getElementById("time");
            labeledItem.focus();
            var result = document.getElementById("result");
            result.innerText = "\nThe accessibility description is \"" + accessibilityController.focusedElement.description + "\"";
        }
    </script>
</body>
</html>