(Re-)Escaping entities in input text

Hi,

I was wondering whether there is an efficient way of "reescaping" the data read from the input file when saving it to an xs:string...

Here's the problem: my input is an XML file which contains text nodes, which in turn may contain escaped entities like &lt; (&amp;lt;) and such. Upon reading it, xsl:value-of (AFAIK) automatically converts these to the corresponding characters '<' etc -- this is completely transparent to the user agent, and in most cases this is sensible. However, in my case, I'm building a string which is actually XML code and whose text nodes are the nodes I've found in my input file. This XML string is then passed on to an external processor (Java class) for further processing. That means, whatever was escaped in my input file should still be escaped in the string, otherwise the string might not be well-formed, and my external processor won't be able to parse it. 

Of course, there is the possibility of replacing all 5 entities "by hand" by calling a transform function, however this might not be very efficient when the string is getting big. Is there either:
- a way of disabling entity interpretation with xsl:value-of (actually getting "&lt;" when it's written like this in the input file)
- a function to "reescape" a piece of text so that it's usable in an XML file/string? 

I know XSLT also escapes metacharacters automatically when outputting to a file, but since I'm only working internally with a string, this doesn't apply to me. "disable-output-escaping" is also not a solution, since it does pretty much exactly the contrary from what I'm trying to do... 

thx in advance for any help! :-)

cheers

David