(1) AssignmentDirective.isNestable() looks only if the directive ends with "/> which is simply wrong for assign, local and global directives. assign documentation lists several possible variants of the directive. AssignmentDirective.isNestable() should cover them all and tests need to be added.

(2) It is clear from the usage of ItemSet.getFirstNestableItem(Stack<Item>) that it is supposed to return the last (as measured by time) item stored at the stack, not the first one. Therefore, getFirstNestableItem() needs to use a reverse order when iterating over the stack.

These two issues should fix the improper tree presented in outline (when rendered with OutlineContentProvider.fullAstShown.