From Comments on XML Documentation (C # Programming Guide):
When compiling with the / doc option, the compiler will look for all the XML tags in the source code and create an XML documentation file.
Also XML comments used by Visual Studio for IntelliSense:
public class MyClass{}
They will give you nice hints when you enter the code or hover over an element with xml comments:

. xml . , , . GhostDoc ( Visual Studio), XML . , - , .
(-xml) . , , . :
, , .