Search highlighting using xslt 2.0

I would like to use xslt 2.0 to create a search highlighting stylesheet.
Matching single words is simple enough, but what about sentence matching
across elements.

For example, consider:

<p>This car has <b>170</b>bhp.</p>

..and the string to match is '170bhp'.  The required output would be:

<p>This car has
<b><highlight>170</highlight></b><highlight>bhp</highlight>.</p>

Or

<p>This car has <highlight><b>170</b>bhp</highlight>.</p>

This seems quite a task, has anyone attempted anything along these
lines?

cheers
andrew