MrpRelation represents a task predecessor relation in the project. A predecessor relation is used to affect the scheduling of a task relative another task. A relation may have a lag time associated to it, so that a task can be scheduled to start after another task has finished, plus a lag time. A private struct for internal use only. The definition of this structure is not publically available. Object representing a predecessor relation between two tasks. @parent: @priv: The type of relation. @MRP_RELATION_NONE: invalid relation type (unset) @MRP_RELATION_FS: finish to start @MRP_RELATION_FF: finish to finish (unimplemented) @MRP_RELATION_SS: start to start (unimplemented) @MRP_RELATION_SF: start to finish (unimplemented) @relation: @Returns: @relation: @Returns: @relation: @Returns: @relation: @Returns: