Because there is a CLR, debuggers can support programs where the code has been written in different .NET languages, and IDEs (such as Visual Studio.NET) can use the CLR to provide information to the programmer. For example, if you have declared some variable:

ArrayList tArrayList;

then, when you start to type the code to apply a method to tArrayList:

tArrayList.

as soon as you type the dot, the IDE can provide you with a pop-up window displaying a list of methods that can be applied to tArrayList.