As specified in RFC 6410:

   (1) There are at least two independent interoperating implementations
       with widespread deployment and successful operational experience.
       
       - Over 98% of all digital network printers shipped in the last
       decade support IPP/1.1 (originally defined in RFC 2910/2911,
       September 2000).

   (2) There are no errata against the specification that would cause a
       new implementation to fail to interoperate with deployed ones.
       
       - There are currently no errata against RFC 8010/8011.

   (3) There are no unused features in the specification that greatly
       increase implementation complexity.
       
       - There are no unused features in RFC 8010/8011.
       
       - The Purge-Jobs operation (from RFC 2911) is DEPRECATED in
       RFC 8011 (page 73) with "SHOULD NOT support" because it
       destroys Printer accounting implementation.  This operation
       has never been widely implemented in digital network printers.

       - The Restart-Job operation (from RFC 2911) is DEPRECATED in
       RFC 8011 (page 89) with "SHOULD NOT support" because it
       destroys Printer accounting implementation.  This operation
       has never been widely implemented in digital network printers.       

   (4) If the technology required to implement the specification
       requires patented or otherwise controlled technology, then the
       set of implementations must demonstrate at least two independent,
       separate and successful uses of the licensing process.
       
       - There is no patented or otherwise controlled technology that
       is required to implement IPP/1.1 per RFC 8010/8011.