twitter-bootstrap – 网格系统下的push和offset之间有什么区别？

我试图理解推和网格之间的差异。例如，下面两行之间的唯一区别是每一行中的第三列。一个使用推动，另一个使用偏移。然而，它们都渲染完全相同。

<div class="row">
    <div class="col-md-2">
        <h2>Column 1</h2>
        <p>
            This is text for column 1
        </p>
        <p><a class="btn btn-default" href="http://go.microsoft.com/fwlink/?LinkId=301865">Learn more &raquo;</a></p>
    </div>
    <div class="col-md-2">
        <h2>Column 2</h2>
        <p>This is text for column 2</p>
        <p><a class="btn btn-default" href="http://go.microsoft.com/fwlink/?LinkId=301866">Learn more &raquo;</a></p>
    </div>
    <div class="col-md-2 col-md-push-6">
        <h2>Column 3</h2>
        <p>This is text for column 3</p>
        <p><a class="btn btn-default" href="http://go.microsoft.com/fwlink/?LinkId=301867">Learn more &raquo;</a></p>
    </div>
</div>

<div class="row">
    <div class="col-md-2">
        <h2>Column 1</h2>
        <p>
            This is text for column 1
        </p>
        <p><a class="btn btn-default" href="http://go.microsoft.com/fwlink/?LinkId=301865">Learn more &raquo;</a></p>
    </div>
    <div class="col-md-2">
        <h2>Column 2</h2>
        <p>This is text for column 2</p>
        <p><a class="btn btn-default" href="http://go.microsoft.com/fwlink/?LinkId=301866">Learn more &raquo;</a></p>
    </div>
    <div class="col-md-2 col-md-offset-6">
        <h2>Column 3</h2>
        <p>This is text for column 3</p>
        <p><a class="btn btn-default" href="http://go.microsoft.com/fwlink/?LinkId=301867">Learn more &raquo;</a></p>
    </div>
</div>