<body style="margin: 0">
<div style="margin: 50px; background-color: lightblue; width: 800px; height: 200px; -webkit-column-width:185px; -webkit-column-gap:15px; -webkit-column-fill:auto; column-width:185px; column-gap:15px; column-fill:auto; font-family: Ahem; font-size: 50px; line-height: 1;">
    123<div style="background-color: blue; height: 70px;"></div>abc<br>def<div style="background-color: blue; height: 60px;"></div>ghi<br>jkl<div style="background-color: blue; height: 110px;"></div>mno</div>
<pre id="console" style="display: none;"></pre>
<script>
    function characterAtPoint(x, y)
    {
        var range = document.caretRangeFromPoint(x, y);
        if (range.startContainer.nodeType !== Node.TEXT_NODE)
            return null;
        if (range.startOffset >= range.startContainer.length)
            return null;
        return range.startContainer.data[range.startOffset];
    }

    function log(message)
    {
        document.getElementById("console").appendChild(document.createTextNode(message + "\n"));
    }

    function test(x, y, character)
    {
        var actualCharacter = characterAtPoint(x, y);
        if (character === actualCharacter)
            log ("Character at " + x + ", " + y + " is " + character + " as expected.");
        else
            log ("FAIL: Character at " + x + ", " + y + " is " + actualCharacter + ". Expected " + character + ".");
    }

    if (window.testRunner)
        testRunner.dumpAsText();

    test(150, 25, "1");
    test(350, 25, "d");
    test(550, 25, "j");
    test(750, 25, "m");

    test(150, 275, "d");
    test(350, 275, "j");
    test(550, 275, "m");
    test(750, 275, null);

    test(150, 475, "d");
    test(350, 475, "j");
    test(550, 475, "m");
    test(750, 475, null);

    document.getElementById("console").style.display = "block";
</script>