In description.ext (or any config.cpp), add:
class parentclass {
value = 1;
text = "STRING";
};
class myclass : parentclass {};
Then try following in debug console:
count (missionconfigfile >> "myclass"); // returns 0
"true" configClasses (missionconfigfile >> "myclass"); // returns []
(missionconfigfile >> "myclass") select 0; // will lead into script error