In Visual C# you can create documentation for your code by including XML tags in special comment fields in the source code directly before the code block they refer to. For example:

/// <summary>
///  This class performs an important function.
/// </summary>
public class MyClass{}

When you compile with /doc the compiler will search for all XML tags in the source code and create an XML documentation file. To create the final documentation based on the compiler-generated file, you can create a custom tool, or use a tool such as Sandcastle.

Note:
The XML doc comments are not metadata; they are not included in the compiled assembly and therefore they are not accessible through reflection.