It is probably the easiest if you put a #halt somewhere and stop trough the code, then you see what actually happens. To explain it in words: you are walking over the wiki document AST. It has leaf (PRText, PRAnchor, PRHorizontalRule, ...) and non-leaf nodes (PRParagraph, PRTableCell, PRFormat, ...). All the non-leaf nodes are subclasses of PRDocumentGroup that defines the logic for child-elements. Now in the visitor, if you have for example a look at PRWikiWriter>>visitHorizontalRule: anObject self newLine; nextPutAll: anObject class markup With PRParagraph this looks different: PRWikiWriter>>visitParagraph: anObject self newLine. super visitParagraph: anObject If you have a look at the super implementation you see it delegates (along its hierarchy) to PRVisitor>>visitParagraph: anObject self visitDocumentGroup: anObject and finally to PRVisitor>>visitDocumentGroup: anObject self visitAll: anObject children So it is used to get the default behavior of the superclass, what is "visit my children" in this case. All visitors basically delegate along their hierarchy to get default behavior. In rare cases I use shortcuts (for example the search), to avoid walking trough the whole model. So, not implementing means default behavior. Calling super means added behavior + default behavior. Does that make sense? Lukas -- Lukas Renggli http://www.lukas-renggli.ch