In WF 4.0, a bookmark is a mechanism that enables an activity to wait for an input without interrupting a workflow thread. When an activity signals that it is waiting for the input from a user, it can create a bookmark. A bookmark is created by using the BookmarkOptions class. This class provides the following bookmark types:
None - Represents a bookmark that can be resumed exactly once. This is the default bookmark type.
MultipleResume - Refers to a bookmark that you can resume multiple times.
NonBlocking - Refers to a bookmark that does not block the functioning of the workflow.