[xsl] Check for duplicate @id's - collection()

["Philip Vallone" <philip.vallone@xxxxxxxxxxx>]

Hi,
 
I have a project were I take about 800 files and transform them into one .fo
document (create a pdf). The files are authored independent of each other
(stand alone) which are validated against a schema (independently). If there
is a duplicate @id attribute, the validator will tell me. However, the @ids
need to be unique across all files processed by the collection function. If
they are not, my resulting .fo will have duplicate @ids, which cause FOP to
halt.

I am looking for a way to (query or xslt 2.0) to check for duplicate @id's
values across all files with the collection function. This would be a
pre-production check.

I am looking for ideas or suggestions. Also, I am using Saxon 9.1.0.1

Thanks,

Phil