Description.ext:

class X
{
	#include "\userconfig\somefile.hpp"
};

Userconfig\somefile.hpp:

class Y
{
	key = value;
};

Script:

ucval = [[getNumber]] ([[missionConfigFile]] >> "X" >> "Y" >> "key");

Skipping class X means the user could introduce anything into the description.ext Note that #include WILL fail with a CTD if the somefile.hpp doesn't exist.

missionConfigFile is used when the mission does the include from description.ext

campaignConfigFile is similar but for a campaign

configFile is about the “global config” of unit types, vehicle types, and so on, this is the area added to by addons.