ModuleExecObjects are a little like Fuses and Daemons in that they allow code to be executed at a particular point, although a ModuleExecObject is not the really same thing as a Fuse or Daemon. Instead, ModuleExecObject is an abstract base class for various classes that provide modular execution hooks. This class and its subclasses are mix-in classes - they can be multiply inherited by any object (as long as it's not already some other kind of module execution object).
The point of the Module Execution Object and its subclasses is to allow libraries and user code to define execution hooks, without having to worry about what other libraries and user code bits are defining the same hook. When we need to execute a hook defined via this object, we iterate over all of the instances of the appropriate subclass and invoke its execute() method.
By default, the order of execution is arbitrary. In some cases, though, dependencies will exist, so that one object cannot be invoked until another object has already been invoked. In these cases, you must set the execBeforeMe property to contain a list of the objects whose execute() methods must be invoked before this object's execute() method is invoked. The library will check this list before calling execute() on this object, and ensure that each object in the list has been invoked before calling this object's execute(). Similarly, you can use the execAfterMe property to contain a list of all the ModuleExecObjects that mustn't execute until the current object has executed.