substring for whole words.

I'm sure I'm just missing something obvious, but how do I get
substring-before() or substring() to not split something in the
middle of a word.  What I mean is, given an xml snippet of:

<foo>
<wibble>This is only a test but it is a really really long
one</wibble>
<wibble>This is a different test, right.</wibble>
</foo>

How do I produce:
<ul>
<li>This is only a test</li>
<li>This is a different test</li>
</ul>

I.e. Take the first five words as delimited by the whitespace?
Any Hints?

Many Thanks,
James Cummings


-- 
Dr James Cummings, James.Cummings@xxxxxxxxx, http://www.uea.ac.uk/~q503
Cursus Project, School of Music, University of East Anglia,
Norwich, Norfolk, NR4 7TJ, UK  Tel:(01603)593-595



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