Workflow starts a long running processing from the browser and the browser maintains the state of it. All instances of workflow is persisted on the browser and it allows to restore them if user revisits the same view.
This example has the most information of base feature, and there is another sample on unit tests at core/workflow such as persistent-workflow.spec.ts, persistent-workflow-step-one.spec.ts, persistent-workflow-step-two.spec.ts, persistent-workflow-step-three.spec.ts.
To try this example, after input a target computer name in below textbox, click actions and see notifications. You can refresh the browser during the operations and click restore to restore the workflows.