> My XML document has a specific encoding.
>
>   <?xml version="1.0" encoding="ISO-8859-1"?>
>   <document>data goes here</document>
>
> What XSL do I use to read the value of the encoding attribute?

You can't. By the time the XML parser has done its work, the original
encoding of the file is of no further interest, since all the characters are
now in Unicode.