Definition: Indicates that the subject Act has undergone or should undergo substitution of a type indicated by Act.code.
\nRationale: Used to specify "allowed" substitution when creating orders, "actual" susbstitution when sending events, as well as the reason for the substitution and who was responsible for it.
\nhttp://terminology.hl7.org/CodeSystem/v3-ActClass
where concept is-a SUBST