This field is optional when using a custom marshaler.

You can set this field to a string that supplies additional information to a custom marshaler. For example, the same marshaler can be used to provide a number of wrappers, where the cookie is used to indicate the specific wrapper.

Namespace: System.Runtime.InteropServices
Assembly: mscorlib (in mscorlib.dll)
Assembly Versions: 1.0.5000.0, 2.0.0.0, 4.0.0.0