SFINAE

Function templates participate in name resolution for overloaded functions, but the rules are different. For a template to be considered in overload resolution, the type has to match exactly. If the types do not match exactly, the conversions are not considered and the template is simply dropped from the set of viable functions. That's what is known as "SFINAE" — Substitution Failure Is Not An Error.

dynamic_cast prerequisite

A dynamic cast is performed run-time. A prerequisite for using the dynamic cast operator is the existence of at least one virtual member function in the base class.