ARP0 is the original version of the ARP RDF/XML parser in jena-core.
It has been not been the default RDF/XML parser since Jena 4.8.0 (2023-04).

ARP1 is the parser converted to use the IRIx abstraction and to integrate into the RIOT parser framework.
ARP1 was used as the RDF/XML parser in Jena 4.8.0, 4.9.0, and 4.10. ARP0 was deprecated in these versions. ARP1 was deprecated at Jena 5.0.0 (2024-02).

RRX (SAX variant) is the default RDF/XML parser since Jena 5.0.0.