1. A method comprising: associating plural change events with corresponding listeners, wherein the plural change events represent distinct groups of one or more changes made to a collection of items; in response to a further change of the collection of items, modifying, by a system having a processor, the plural change events to include the further change; notifying, by the system, the listeners of the modified change events; and associating with the collection an ordered list of registered listeners and a mechanism for indicating that a given listener is up-to-date, wherein the ordered list of registered listeners comprises a first portion including not-up-to-date listeners and a second portion including up-to-date listeners, and wherein associating the collection with the mechanism for indicating that the given listener is up-to-date comprises: if a second listener in the ordered list is up-to-date, positioning the given listener in a position following the second listener in the ordered list, if no listener in the ordered list is up-to-date, positioning the given listener at an end of the ordered list and noting that the given listener is the first up-to-date listener in the ordered list.