Hi, I have a tool wrapper with a <param> of type="data". Currently, this renders as a text box with a drop down list that has 52 items in it (the number of things I have in my history, I guess). I'd like to filter this list so that only some items in the history (in my case any item whose name ends with '.rda') are shown in this dropdown. It seems like maybe the 'format' parameter to the 'param' tag is what I want, but: 1) I tried format="rda" and that didn't seem to change anything. 2) "rda" is not in the datatypes.conf file which the documentation suggests is required? (.rda is an extension used for serialized R objects.) The tool I'm working on only accepts rda files as input and the reason I'm asking for this is that it is all too easy to accidentally feed it a file of some other type. If the dropdown could be filtered so that only items which will work with the tool are shown, that would be great. Is there a way to do that? Thanks, Dan