Depends. If you are used to passing subroutine references around or to a declarative style of programming it should be a no-brainer. If you are set on the procedural thinking, it takes some brain rewiring. In this particular case the implementation really is simple. You load the module, you define the object with just a single custom rule that copies the $_[1]->{EXT} to $_[1]->{_content} and returns the $_[0] => $_[1] pair and then call the filter() or filterfile() method. It's all documented. Try and ask if you do not understand something or if something does something unexpected.