This is a reusable definition. Requiredness is relative to this structure; its use and conditions in a message remain on that message's page. Version links browse the other dictionary, not an assumed equivalent component.
Must be specified if a Future or Option. If a Future: UnderlyingSymbol, UnderlyingSecurityType, and UnderlyingMaturityMonthYear are required. If an Option: UnderlyingSymbol, UnderlyingSecurityType, UnderlyingMaturityMonthYear, PutOrCall, and UnderlyingStrikePrice are required.