For superclasses, you must use is:, not c:/classname:, as that is an exact match that doesn’t account for inheritance:
For example, is:LuaSourceContainer will find everything that can contain Luau code (Scripts, LocalScripts and ModuleScripts), while c:LuaSourceContainer will return nothing as you cannot create one on its own, which is the same thing as searching for c:BasePart or c:Instance.
c:/classname: checks the .ClassName property, while is: calls :IsA.