Here's a bit from my init routine (the ::desc package variables contain the ASN.1 descriptions; the _asn variables are class data (so I don't have to re-prepare the ASN.1 descriptions over and over) - I can send the whole module if you'd like):

    my $asn_ext = Convert::ASN1->new;
    $asn_ext->prepare( $Biblio::ILL::ISO::1_0_10161_13_3::desc );
    # some error checking here, snipped for brevity

    $_asn = Convert::ASN1->new;
    $_asn->prepare( $Biblio::ILL::ISO::asn::desc );
    # some error checking here, snipped for brevity
    $_asn_initialized = 1;

    # "1.0.10161.13.3" is what it *should* be, according to the ISO 10
+161 maintenance agency:
    #$_asn->registeroid("1.0.10161.13.3",$asn_ext->find("APDU-Delivery
+-Info"));
    # "1" is what it *is*, by looking at a hex dump of the request rec
+ord
    $_asn->registeroid("1",$asn_ext->find("APDU-Delivery-Info"));
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The encode routine:

sub encode {
    my $self = shift;
    my $href = $self->as_asn(); # builds a Convert::ASN1-parsable hash
    my $asn = $_asn->find( 'ILL-Request' ) or warn $_asn->error;
    my $pdu = $asn->encode( $href ) or warn $asn->error;
    return $pdu;
}
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And the decode routine:

sub decode {
    my $self = shift;
    my $pdu = shift;
    my $asn = $_asn->find( 'ILL-Request' )
        or warn $_asn->error;
    my $href = $asn->decode( $pdu ) or warn $asn->error;
    return $href;
}
[download]

I *think* the question is: How do I, in the middle of an 'ILL-Request' decode, tell it to find('APDU-Delivery-Info') when/if it encounters that extension code?

Of course, I could be completely misunderstanding the way that Convert::ASN1 works. :-)

Oops, that was me (bibliophile) - I forgot to log in, sigh.