http://openehr.org/releases/AM/latest/docs/ADL2/ADL2.html#_validity - references
SARID: archetype identifier validity. the identifier of the artefact must conform to the ARCHETYPE_ID identifier syntax defined in the openEHR.Support IM Specification.
This has been moved to openEHR.Base - http://openehr.org/releases/BASE/latest/docs/base_types/base_types.html#_identification_package - as you are told at http://openehr.org/releases/RM/latest/docs/support/support.html#_identification_package
The link in the ADL2 document should be updated accordingly.
Fixed a while ago, but not sure when exactly.