String Manipulation - Distinguishing alphas and numeri

Does anyone know how to do this? (the chemistry is not the issue, I realize
this is a bogus combination)


XML source: 
<para>candybars are made of <chemical>H20ClF3</chemical>.</para>


XSL needed?????
<xsl:template match="chemical">
  <xsl:variable name="this_chemical" select="."/>

<!-- This is the part I'm stuck on. How do I process the string? The
translate function only wants to replace something. How do I walk through
the string and wrap each number with the FO for subscript? -->

</xsl:template>

XSL-FO desired:

<fo:block>water is made of H<fo:inline baseline-shift="sub"
>2</fo:inline>OClF<fo:inline baseline-shift="sub" >3</fo:inline>.</fo:block>

Thanks,

Kevin

 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list