What exactly is a “Special Class”?

Question

After failing to get something like the following to compile:

public class Gen where T : System.Array
{
}

with the error

Answer 1

According to MSDN it's a static list of classes:

Compiler Error CS0702

Constraint cannot be special class 'identifier' The following types may not be used as constraints:

• System.Object
• System.Array
• System.Delegate
• System.Enum
• System.ValueType.