negate predicate

I want to select the text of all descendants of a node which *don't*
have an attribute called 'id' (and none of the nodes which are
descendants of nodes with id attributes).

So that, from the following document snipet:

<document>
    <section id="first">
        <p>Hello, foo bar</p>
        <subsection id="bar">
            <p>Some stuff</p>
        </subsection>
        <subsection id="foo">
            <p>Some other stuff</p>
        </subsection>
    </section>
    <section id="second">
        <subsection id="qwerty">
            <p>More text</p>
        </subsection>
        <p>words, words</p>
    </section>
</document>

an XPath expression like:

//section//*[@id = '']/text()

would return: "Hello, foo barwords, words"

and one like:

//subsection//*[@id = '']/text()

would return: "Some stuffSome other stuffMore text"

(I realise that here I could just tell it not to select 'subsection'
elements but my real document has a more complex hierachy including
structural elements which share names with formatting elements [and
which are only distinguished by having an 'id' attribute]).

Thanks for your help,
Richard
-- 
  Richard Lewis
  richardlewis@xxxxxxxxxxxxxx