SRU::Response::Diagnostic - An SRU diagnostic message
my $d = SRU::Response::Diagnostic->new( uri => '', details => '' message => '' ); print $d->asXML();
You probably won't need to use this class since it used interally to store diagnostic messages.
Pass in uri, details and message attributes as needed. You'll probably find using newFromCode() easier to work with.
Create a SRU::Response::Diagnostic object from a code. For a complete list of the codes see the SRW/SRU documentation.