[xsl] How to show context of term in text document?

[Antony Quinn <aquinn@xxxxxxxxx>]

Hello,

I would like to display the context in which a term appears in some 
text, in the same way that Google shows the 5 or so words before and 
after your search term in the document.

Example
-------

For this input:

<s id="39">
  The aforementioned oxygenated
  <z:e sem="chebi" ids="33284">nutrient</z:e> emulsion (using the
  fluorocarbon FC-80) was placed in a Harvey pediatric oxygenator
  (volume 1230cc) and maintained at about 40 DEG C
</s>

I want to show the 5 words before and after "nutrient":

... The aforementioned oxygenated *nutrient* emulsion (using the 
fluorocarbon FC-80) ...

Any ideas?

Thanks,

Antony