The Cer enumeration specifies the behavior of a method, type, or assembly within a constrained execution region (CER). Use one of the three available values to indicate that the entity will succeed, has no knowledge of a CER, or might (deterministically) be able to report success or failure.
A CER provides guarantees that the region of code will execute uninterrupted even if an asynchronous exception such as an aborted thread out-of-memory exception, or stack overflow is raised.