how to translate XML with XHTML-formatted element to F

how can I translate XML files (like the following), which contain
XHTML-formatted text in one element, to PDF using Apache FOP ?

 --- books.xml --->
 <BOOK>
   <AUTHOR>Walt Disney</AUTHOR>
   <PRICE>19.90</PRICE>
   <TITLE>&lt;b&gt;Donald Duck - &lt;i&gt;The True Story&lt;/i&gt;
&lt;/b&gt;</TITLE>
 </BOOK>

 <BOOK>
   <AUTHOR>Matt Groening</AUTHOR>
   <PRICE>25.00</PRICE>
   <TITLE>&lt;b&gt;Homer Simpson For President&lt;/b&gt;</TITLE>
 </BOOK>
   ...
 <--- books.xml ---

I mean how should an appropriate XSL stylesheet be designed best to handle
straight forward FO formatting for <AUTHOR> and <PRICE> as well as for
additional transformation of XHTML-formatted <TITLE> ?

I just need some general ideas on how I can process XML files with
sub-structured (XHTML-formatted) elements by one (or more) XSL
stylesheet(s).

My problem is not to translate XHTML-formatted text to FO resp. PDF (for
this purpose I already have a working "xhtml-to-fo.xsl" stylesheet).
Rather I have no idea at the moment on how to integrate the existing
xhtml-to-fo.xsl code and templates into the main XSL stylesheet for
generating the FO output.

Currently I'm only able to translate content of <TITLE> element as plain
text to FO output, i.e. FO output for <TITLE> shows the tags <b>...</b> and
<i>...</i> as is, without applied bold and italic formatting on title text.

Best regards,
Maik