One example in C++ has to do with formal types in templates. Consider the following example:
template <class Type> class A { private: Type *p; }
In order that the class definition be typeset correctly, ‘Type’ must be understood to be a reserved word like int, and that is correctly figured out by the first class command. However, according to C++, the scope of ‘Type’ is local to the class definition; unfortunately, FWEAVE does not respect that locality and will always treat ‘Type’ as an int from the point of the ‘class Type’ construction to the end of the source code. Thus, one should use such dummy variables as ‘Type’ only as formal template parameters, never as ordinary variables.