DOMXPath根据先前的兄弟值获取兄弟姐妹

Let's say I have this:

假设我有这个:

<foo>
    <bar>CCC</bar>
    <baz>sometexthere</baz>
</foo>
<foo>
    <bar>AAA</bar>
    <baz>sometext</baz>
</foo>
<foo>
    <bar>DDD</bar>
    <baz>something</baz>
</foo>
<foo>
    <b