Designates a modifier to the code attribute to provide additional information about the invoice element.

Examples: Isolation allowance; After-hours service

Rationale: This is not pre-coordinated into the CD attribute because the modifier code set may not be specifically designed for use with the Act.code code set. This violates the constraint for using the 'modifier' property that the modifier code set must be defined as part of, or specifically for the base code set.