Function with_der_reader 

pub fn with_der_reader<X: BinaryXml, R, C>(
    xml: &X,
    location: Location<X::Id, X::Document, X::Generation>,
    operation: &Reader<'_>,
    visitor: impl for<'source> FnOnce(&mut Reader<'source>) -> Result<R, C>,
) -> BinaryResult<R, X, C>

Visits a schema-fixed DER value, such as IssuerSerialV2 (§5.2.2). An unrelated XML attribute cannot make this ASN.1 value permissive BER. Outer XML schema/attribute validation remains a separate obligation.