14.1 Language Support

Decorating an element with a custom attribute is known as specifying the custom attribute. This is done by writing the name of the attribute enclosed in brackets ([ ]) immediately before the element declaration as follows:

[Serializable] public class Foo {...}

In this example, the Foo class is specified as serializable. This information is saved in the metadata for Foo, and affects the way the CLR treats an instance of this class.

A useful way to think about custom attributes is they expand the built-in set of declarative constructs in the C# language, such as public, private, and sealed.