parsing string or numbers after x characters

Hello

I'm quite new to the xsl mailing list so I have no idea if this problem 
occurred already and I was unable to find the solution on the web.

My problem is that I receive for example a date in a concatenated format:

Ex: 20041207

And I have to retrieve it in a readable format through my xslt-fo 
transformation.

Ex. 12 July 2004

I tried using the substring attribute for that, but I don't have any 
reference character to look at so it doesn't work. Is there a function 
which parses strings or numbers after a certain amount of characters 
directly?

Thanks in advance for those which will response.


Julien