[xsl] Isolate spezial text term with pattern

["KrustyDerClown" <KrustyDerClown@xxxxxx>]

Hello,

i have the following XML document (not complete):

<document>
  <report>
     <comment>Hallo commentar. PB123</comment>
  </report>
  <report>
     <comment>Hallo commentar. PB456</comment>
  </report>
   ......
</document>

What i now what to do is the following: I will islote the terms "PB123" and 
"PB456" and so on in the hole document. Therefore i need a spezial pattern i 
think. The pattern is always the same: "PB" and then 3 or 4 numbers. I will 
write this terms in an extra column in a HTML table.

How i get the text from <comment>...</comment> is clear for me. Thats no 
problem.

I hope you know what i need. :)

Thank you for your support.

Greets Oliver