According to this table of terminal emulators and their keycodes, new versions of XTerm recognize function keys from F1, F2, F3, ... all the way up to F63. Most keyboards only have physical function keys in the range F1..F12. What is the purpose of the extra keys? Is there some (semi-)standard mapping from physical key or mouse presses to those function key numbers, and if not, how are they triggered?

I'm under the impression that in traditional terminal parlance, all special keys including the arrow keys, home/end, etc. were called function keys (whereas those of us who grew up on PCs would consider only F1..F12 to be function keys). But then, XTerm also talks separately about these named keys (e.g. kUP for the up arrow key in that table).