Starting from tc-2.4 the boot sequence takes the dep files in the /tce folder into account if present.
Taking dbus.tczl.dep as an example, since it contains expat2.tczl, it means that expat2 will be loaded before dbus. If this dep file is not present, the boot sequence will load in alphabetical order and since expat2 is required for dbus to start, the start-up script for dbus will fail.