Variables in the domains should be ordered with identifiers first, followed by the topic, qualifier, and timing variables.
SEND
Additional timing variables (see SDTM v1.5 Table 2.2.5; https://www.cdisc.org/standards/foundational/sdtm/) can be added as needed to a standard domain model based on the 3 general observation classes. Timing variables can be added to special-purpose domains only where specified in the SENDIG domain model assumptions. Timing variables cannot be added to SUPP-- datasets or to RELREC (see Section 8, Representing Relationships and Data). Timing variables cannot be added to the Trial Design Model datasets (see Section 7, Trial Design Model Datasets).