A node instance represents the execution of one specific node
in a process instance. Whenever a node is reached during the
execution of a process instance, a node instance will be created.
A node instance contains all the runtime state related to the
execution of that node.
Multiple node instances for the same node can coexist in the same
process instance (if that node is to be executed multiple times
in that process instance).
A node instance is uniquely identified (within its node instance
container!) by an id.
Node instances can be nested, meaning that a node instance can
be created as part of another node instance.
The node instance container that this node instance is part of.
If the node was defined in the top-level process scope, this is
the same as the process instance. If not, it is the node instance
container this node instance is executing in.
the process instance that this node instance is executing in