The concat result child extends, or undefined when it extends nothing: a view change (new generation), the first loaded level, or a restored-from-cache clone. The append gate treats undefined as "not an append" and forces a full rewrite.
child
undefined
The concat result
childextends, orundefinedwhen it extends nothing: a view change (new generation), the first loaded level, or a restored-from-cache clone. The append gate treatsundefinedas "not an append" and forces a full rewrite.