What happens when a button in the navigation bar is pressed?
This is described in Appendix I of the User Guide to the Menu and Security (RBAC) System. It may be completely obvious, but it should be pointed out that it would not be a good idea to create a navigation button for a child task which is unable to use the context which is passed down from the parent task. For example, if the parent task passes down a $where/$selection string containing values for field names which do not exist on the child table, and the child task is unable to convert that string into anything which it can use, then the child task will always fail to read anything from the database.
