The PEP has this section: > The new operators will have the same relationship to the dict.update method as the list concatenate (+) and extend (+=) operators h

The PEP has this section: > The new operators will have the same relationship to the dict.update method as the list concatenate (+) and extend (+=) operators have to list.extend. Note that this is somewhat different from the relationship that |/|= have with set.update; the authors have determined that allowing the in-place operator to accept a wider range of types (as list does) is a more useful design, and that restricting the types of the binary operator's operands (again, as list does) will help avoid silent errors caused by complicated implicit type casting on both sides. Would someone please explain what they mean with regard to being different from set.update, and what could lead to silent errors?