This appendix is not part of the standard definition of the Ada programming language.
The Ada language definition allows for certain machine-dependences in a controlled manner. No machine-dependent syntax or semantic extensions or restrictions are allowed. The only allowed implementation-dependences correspond to implementation-dependent pragmas and attributes, certain machine-dependent conventions as mentioned in chapter 13, and certain allowed restrictions on representation clauses.
The reference manual of each Ada implementation must include an appendix (called Appendix F) that describes all implementation-dependent characteristics. The appendix F for a given implementation must list in particular:
(2) The name and the type of every implementation-dependent attribute.
(3) The specification of the package SYSTEM.
(4) The list of all restrictions on representation clauses (see 13.1)
(7) Any restriction on unchecked conversions (see 13.10.2).