Workflows, activities, and rules can be serialized and deserialized. This enables you to persist them, use them in workflow markup files, and view their properties, fields, and events in a workflow designer.
Windows Workflow Foundation provides default serialization capabilities for standard activities, or you can create your own for custom activities. For example, with a custom activity serializer, you can decide which members are serialized and how they are serialized. This determines if those members are visible or hidden in a workflow designer.