I'm referring to the module that I discussed in Re: Runtime introspection: What good is it?.

For example in one place in my current reporting framework I have a way that objects from lots of modules can be passed into a particular method in another module. There are several useful methods that they might implement. When I load the first module I don't know what others might exist and I don't know what will be passed in, so I leave the decision as to whether to call the method to run time where I check that the method exists by calling can, and then do one thing if it does and another if it doesn't.