class SequenceDataDefinition

class SequenceDataDefinition extends ListDataDefinition {
    
    /**
     * Gets the description of how the sequence should be sorted.
     *
     * Only the top level of the array should be sorted. Top-level keys should be
     * discarded when using 'value' sorting. If the sequence is an associative
     * array 'key' sorting is recommended, if not 'value' sorting is recommended.
     *
     * @return string|null
     *   May be 'key' (to sort by key), 'value' (to sort by value, discarding
     *   keys), or NULL (if the schema does not describe how the sequence should
     *   be sorted).
     */
    public function getOrderBy() {
        return $this->definition['orderby'] ?? NULL;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getDataType() {
        // TRICKY: this class extends ListDataDefinition, which always returns a
        // hardcoded "list". But this is a typed data type used in config schemas,
        // and hence many subtypes of it exists. The actual concrete subtype must
        // always be returned.
        // This effectively means skipping the parent implementation and matching
        // the grandparent implementation.
        // @see \Drupal\Core\TypedData\ListDataDefinition::setDataType()
        // @see \Drupal\Core\TypedData\ListDataDefinition::getDataType()
        return $this->definition['type'];
    }

}