(Probably trivial) grouping problem

I can't for the life of me figure out how to solve a simple problem. I 
know that it is related to grouping, but my XSL (and XPath) knowlegde is 
not up to translating answers given to similar problems to my particular 
case. 

I have a couple of paragrahps, marked up this way:

<para title="title1">
        some text
</para>
<para>
        a para without a title
</para>
<para title="title2">
        more text
</para>
<para>
        yet another untitled para
</para> 

I want to turn them into this:

<section>
        <title>title1</title>
        <para>
                some text
        </para>
        <para>
                a para without a title
        </para>
</section>
<section>
        <title>title2</title>
        <para>
                more text
        </para>
        <para>
                yet another untitled para
        </para> 
</section>

That is, I want to create sections from paragraphs, turning the title into 
an element belonging to the section. My experiments with following-sibling 
and preceeding-sibling all had the problem that *all* paragraphs without a 
title were returned, and I somehow need to get access to only those before 
the next para with a title. 

Any help would be greatly appreciated.

Stefan

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