[Pharo-project] Why has MethodFinder a fixed list of results?

Dear list, I was showing off Pharo to a colleague today and was surprised that. My quick introduction of adding new methods on existing system classes String>>firstLetter ^self copyFrom: 1 to: 1 - extension on String worked immediately. But that: in the MethodFinder evaluating: 'tried'.'t' did not return my method I just added .... :-( Turns out that MethodFinder has a class side Set of Approved and AddAndRemove methods. What is the rationale of this? Should we not allow any method, but exclude some tricky ones (doesNotUnderstand:, ... )? Kind Regards, Bart