<script>

    function toggleDisplay(element, button)

    {

        if (element.style.display == "none")

            element.style.display = "";

        else

            element.style.display = "none";

    }

    function toggleVisibility(element, button)

    {

        if (element.style.visibility == "hidden")

            element.style.visibility = "";

        else

            element.style.visibility = "hidden";

    }

</script>

<p>

    Play with the display and visibility toggles. Make sure that turning an inner element visible does not show it if it has a hidden or

       non-displaying ancestor, and that making an ancestor visible and displaying shows only its descendants the are visible and displaying.

</p>

<table>

    <tr>

        <td>

            <input type="checkbox" checked="true" onclick="toggleDisplay(document.getElementById('middle'))"> Outer frame display

        </td>

        <td>

            <input type="checkbox" checked="true" onclick="toggleDisplay(document.getElementById('middle').contentDocument.getElementById('inner'))"> Inner frame display

        </td>

    </tr>

    <tr>

        <td>

            <input type="checkbox" checked="true" onclick="toggleVisibility(document.getElementById('middle'))"> Outer frame visibility

            </td>

        <td>

            <input type="checkbox" checked="true" onclick="toggleVisibility(document.getElementById('middle').contentDocument.getElementById('inner'))"> Inner frame visibility

        </td>

        <td>

            <input type="checkbox" checked="true" onclick="toggleVisibility(document.getElementById('middle').contentDocument.getElementById('inner').contentDocument.getElementById('plugin'))"> Inner plug-in visibility

        </td>

    </tr>

</table>

<iframe id="middle" style="height: 400px; width: 400px;" src="resources/nested-plug-ins-outer-frame.html"></iframe>