if there is no admin for the parent, the method returns early, no? i think adding a show or unlinked item can be useful to understand where in the tree we are.

the parameter should be something like cmf_menu.persistence.phpcr.max_breadcrumb - a default of 5 sounds reasonable. that means after 3 iterations we would have to stop and only show the root document (i.e. menu or some generic node). position number 5 is the item itself. i think its most logic for the end user if he specifies how many things he wants in the breadcrumb, and not how many iterations we do here.