The node needs to complete dirty itself during regeneration and produce new work items.
Something about the node itself has changed, e.g. a parm and the node needs to be regenerated. Dynamic nodes will delete all their work items.
Regeneration is occuring because an upstream node was modified, but nothing about the specified node changed directly.
Partial, except that if PDG encounters this regeneration status
on a node it will also ensure that all outputs are upgraded to the same
status if they're set to
The node is not regenerating at all, and its input nodes have also not been invalidated.