I've been fiddling with this a little bit, and have concluded that it is all simply messed up. You are supposed to be able to start typing in the Search box, and you can then get a drop-down menu of "tokens"--at the moment there are two, Filename or Everything. From the microscopic triangle in the darker blue part you can switch back and forth between the two:
There are several things about this that just don't work right. You must type something before you can select one or the other, and you cannot add to what you started typing when you made your selection, but you can evidently then start typing over again--thus the "g" in the light blue part, followed by "gera" in the still active part of the Search box. So in the above I typed "g" then selected Filename, then started adding more with "gera" to begin narrowing the results--but I still got some items that just don't belong, they are evidently left-over from the plain "g" entry, although MOST plain "g" things don't show up. Just some. If I subsequently add another letter, so that I have "geran" then everything that shows up has all those letters in the file name, and "gallery.jp" and "Genesis.txt" disappear from the results. It just all seems a bit bizarre to me.
Francine