Flags

The following flags affect group rule behavior.

Canonical

The Canonical flag indicates a rule that is computable via one or more Group rules. It is an error if no group rules exist that set the Canonical.

Note: Canonicals can also be inherited from mixins.

Passive

The Passive flag may only be used for parameters. It allows parameters to act as if they are supplied, when determining if a Group rule is computable. It should only be used for parameters whose default value does not depend on the Canonicals it participates in being computable. The rule must have a default value; if evaluated due to Passive activation, an error will be generated if there is no expression.

Note: If more than one group is available, the group that is most specifically selected has the highest priority. Groups that are activated due to Passive rules typically have lower priority.