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chromium/third_party/blink/web_tests/fast/forms/mailto/advanced-put.html 

<!DOCTYPE html>
<html>
    <head>
        <title>action="mailto" PUT method</title>
        <script>
            function test() {
              if (window.testRunner) {
                testRunner.dumpAsText();
                testRunner.waitForPolicyDelegate();
                document.getElementsByTagName("form")[0].submit();
              }
            }
        </script>
        <style>input { width: 100px; } </style>
    </head>
    <body onload="test()">
        <p>Press Compose button and check that the created e-mail has correct headers and body.</p>
        <form action="mailto:" method="put">
            <input name="to" value="[email protected],[email protected],[email protected]">
            <input name="cc" value="[email protected],[email protected],[email protected]">
            <input name="bcc" value="[email protected],[email protected],[email protected]">
            <input name="subject" value="m&amp;m;?=">
<textarea name="body">line1
line2
line3
line4</textarea>
            <input type="submit" value="Compose">
        </form>
    </body>
</html>