Use of Attributes

Attributes are a feature that is familiar to developers who use C++ to write COM components (through their use in Microsoft’s COM Interface Definition Language [IDL]). The initial idea of an attribute was that it provided extra information concerning some item in the program that could be used by the compiler.
Attributes are supported in .NET—and hence now by C++, C#, and Visual Basic 2005. What is, however, particularly innovative about attributes in .NET is that a mechanism exists whereby you can define your own custom attributes in your source code. These user-defined attributes will be placed with the metadata for the corresponding data types or methods. This can be useful for documentation purposes, where they can be used in conjunction with reflection technology in order to perform programming tasks based on attributes. Also, in common with the .NET philosophy of language independence, attributes can be defined in source code in one language, and read by code that is written in another language.

C# provides a mechanism for defining declarative tags, called attributes, which you can place on certain entities in your source code to specify additional information. The information that attributes contain can be retrieved at run time through reflection. You can use predefined attributes or you can define your own custom attributes.