There is one attribute for interoperation with pre-existing native applications; it is platform-specific and shall not be used in code intended to run on multiple implementations of the CLI. The attribute is marshal and specifies that the field's contents should be converted to and from a specified native data type when passed to unmanaged code. Every conforming implementation of the CLI will have default marshaling rules as well as restrictions on what automatic conversions can be specified using the marshal attribute. See also §II.15.5.4.
[Note: Marshaling of user-defined types is not required of all implementations of the CLI. It is specified in this standard so that implementations which choose to provide it will allow control over its behavior in a consistent manner. While this is not sufficient to guarantee portability of code that uses this feature, it does increase the likelihood that such code will be portable. end note]