Use 'createcontext' to create a named document:

<s:createcontext name="mystuff"/>

Use 'setxml' to update a document at an XPath expression's target:

<s:setxml context="mystuff" path="/">
<stuff/>
</s:setxml>

Use 'getxml' to get content at an XPath expression's target:

<s:getxml context="mystuff" path="/"/>