I noticed that .NET framework uses formatting functions, generated the same way localizable string are.

There is a resource file Resources.resx with resource string TestString. So you may use it in code like this:

string localizableValue = Resources.TestString;

Now, imagine you need a formattable localizable string, to use it in string.Format function. So everytime you use it, you have to write something like this:

string localizableFormattedValue = string.Format(Resources.TestFormatString, someParam1, someParam2);

The observation says that in .NET framework generated resource classes already include the above construction. So instead of string property, a string function is generated. The resulting code looks like this:

string localizableFormattedValue = Resources.TestFormatString(someParam1, someParam2);

The question is - how do they do this? Is it some custom Microsoft feature (resx generator) or I'm missing something obvious?