There are several instances where variables defined in the tables are mutually exclusive options of which only one should be requested. The varChoice section is designed to hold this information, but is not yet complete. Examples are between ocean cell volume on a fixed grid for some models and monthly means for others, or between 6 hourly pressure level data on 8 levels vs. 4 levels for different objectives in the HighResMIP request. If the choiceClass in ConfigurationOptionSet the record should be linked to by one or more varChoiceLinkC records. If the choiceClass is RedundancySet the record should be linked to by one or more varChoiceLinkR records.