Firstly, I had the idea of using plugins, and wanted to reuse the name of "stereotypes". The idea I had was using some properties of the file to determine a set of stereotypes that are true for it.
For instance, let's say that a file greater than 10mb is a "big file", or that every file with the extension ".zip" is a zip file.
I've abandonned this idea, at the profit of the concept of "conditions", because it seems to be a lot more reliable. Using stereotypes means that each stereotype must be understood in a really specific way, and I had needed to add a lot of stereotypes, each time I found a new usage.
Now we have conditions and plugins. A plugin is defined by two things: an actions and some conditions.
The action should be done when the conditions are met.