Creating a SOAP request with PHP - how do I add attributes to the XML tags?

I am trying to generate the following XML in my SOAP call:

<CResponse>
    <ID>int</ID>
    <Response Action="Apply">
        <Question ID="$someint">
            <Responses>
                <Response ID="$someotherint" />
                <Response ID="$yetanotherint" />
            </Responses>
        </Question>
    </Response>
</CResponse>

I can create most of the call just fine - I've finally picked up that nested arrays are my friends - but I have no idea how to add those ID="$int" and Action="Apply" attributes to the various tags. I'm sure this is fairly easy, but I just can't figure it out.

TIA.