Hi, #isObsolete is interesting… it used to be that there were two definitions “name of class starts with ‘AnObsolete’. (these checks where inlined everywhere). And #isObsolete was checking “my environment knows my name and the result is me”. -> we refactored the system to use #isObsolete everywhere (one of those unimportant cleanups aka “random refactorings”) Then Yuriy wanted to annotate classes like we can already annotate the AST and Methods. So he added a property API (careful to now use space by storing in a ClassVar). Then Andrei realized that our definition of #isObsolte does not work for anonymous behaviors… so should we go back to “self name beginsWith:”? No! The property interface now allows us to solve this how you think it works: we tag obsolte classes. isObsolete "Return true if the receiver is obsolete." ^self propertyValueAt: #obsolete ifAbsent: false This works, even for anonymous classes. And it is *fast*: [Smalltalk allClasses do: #isObsolete] bench Pharo 3: '147 per second.’ Pharo 4: '95.562 per second’ Marcus