Mozilla's DOCTYPE sniffing (Full Standards Mode)

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

.test1, .test2 { width: 200px; background-color: aqua; border: 1px solid red; }
        .test2 { line-height: 0 }

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<p class="test1"><img /><img /></p>

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<p class="test2"><img /><img /></p>
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<table>
    <tr>
        <td class="test1"><img /><img /></td>
    </tr>
</table>
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<table>
    <tr>
        <td class="test2"><img /><img /></td>
    </tr>
</table>