PRFile, MAFileModel and friends

I am trying to figure out the relation between PRFile, MAFileModel, MAFileDescription, and possibly others. They seem to duplicate a lot of information, such as mimetype and filename. I'm using the Pier-1.2 download. PRFile says it references an instance of MAFileModel, but a lot of test code for seems to get by without an MAFileModel. I've looked for references to the classes, but have found either extremely terse and trivial tests or the setupup for, e.g., defaultCSS. I also don't know which of the classes is intended for display, or how to display them. Initially, I just want to use these to display links to files that are on the disk. Presumably that will use MAExternalFileModel somehow. Later on, I may want to have pseudo files that include the ability to select a format in which to download the file or to display the file inline on the web page. Ross Boylan