Last year I had the pleasure of working with Justin on filling in the WFS 2.0 "FunctionName" information. The WFS 2.0 was just the excuse for me - what I really wanted was a data structure I could ask at runtime about functions, their parameters and any restrictions you would need to know when entering them.
While was able to put this information to use and generate a function list for the GeoTools documentation, it is only today that I got a chance to hook the information into uDig.
Update: Finished up this "FilterViewer" code allowing you to smoothly change between a couple of options.
Out of the box I just had time for a couple of options - ranging from a bit of content assist through to the enable / disable radio buttons shown above.
I also managed to get warning and error reporting working (using cute little icons which you can click to see the message).
If you would like to try this Download a sneak peak of uDig 1.3-SNAPSHOT (a tech preview is available for all the platforms).