[galaxy-dev] Tool creation: how to restrict input dataset selector to appropriate file types?

Hello, I'm running in a strange issue which I cannot seem to find a solution for. In every tool I created from scratch, the input dataset selector does not only include the datasets corresponding to the file types I set in the format="" attribute in the <param> tag in my XML tool file, but instead it includes the whole history contents. I searched in the wiki's tool syntax section to no avail. I believe I stupidly missed something huge there but I'm really confused. What should I do to have the selector's contents appropriate? Here is one of the tools for which I have this issue: http://pastebin.com/XqvSwtMH Thanks, L-A