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Configuration files must be either lists or maps, i.e. a configuration file that contains just a scalar value is invalid. In particular, the configuration schema of config objects is either a
Sequence or a
SchemaCheckTrait validates this by checking whether the typed config objects are instances of
ArrayElement - the common parent class of the two implementations. This is a fairly arbitrary check, though.
What we really are validating is that the schema definition object is traversable. Therefore we should have an interface for typed data objects that are traversable:
ListInterface should extend
ArrayElement should implement it.