This plugin only applies to --outputType and --inputType parameters meaning that XD needs to convert whatever the native type produced by a module to the specified type. A module can produce an XML string natively and set the content-type header to text/xml and no conversion comes into play.  A module that natively outputs byte[] (e.g. file source) can declare --outputType=text/plain (with any valid charset or UTF-8 by default) and XD can perform the conversion. A module producing a Java type may specify --outputType=text/plain and that will invoke toString().  --outputType=text/plain;charset=... should throw an exception because we cannot guarantee a particular charset via toString()

We don't currently support XML conversion. If we do support xml at some point, using JAXB, it would be for  Object<->String, not byte[] to String