Jack,
Slocko gave a few examples of where a phantom key might be used, but he didn't really explain the nuts and bolts of "phantom keys". Quite honestly, to adequately cover it would take pages and pages of description, much of it technical, way more time and space than can be covered here in this forum.
As you know, thru IR we can access the eeprom's of the remotes, and not the actual processor. Most of the remotes come with either 1 K or 2 K eeproms, more the latter. Conceptually you can picture that as like a clerk at the post office standing in front of 2000 mail boxes he can stuff, a sort of matrix with "cubby-holes".
You are also aware that when you set your remote in a device mode, or program your remote upgrade thru KM>IR each device only allows you to assign functions to certain buttons. That's NOT a limnitation of KM, it's a limitation put in by the firmware on the processor chip. Part of that matrix is the "boxes" you can use. If you have a learning remote, part of that matrix is for storing what's learned on the various buttons. Part is for device upgrades and protocol upgrades, and part for macros and keymoves.
As you are well aware, some remotes have more physical buttons than another one does. A huge block is devoted to those physical buttons, and their derivatives, like "shifted buttons". However, not all the space is actually used., there's more space allotted than even that most numerous-buttoned remote.
Thru IR, and the RDF's that were developed for them, some of those unassigned "boxes" in that "buttons" segment can be used as "phantom keys", keys that don't physically exist. However, they can be accessed thru macros.
There use can come in handy for functions we might rarely use. I'll try to give an example that maybe you can follow and find "down home".
Let say you bought a nice Panny big-screen tv(not a wide-screen model). OK, you got that cuz you like nice big normal formatted pictures. You Don't want to "Waste" almost a third of your screen with black bars top and bottom by using that "silly" 16:9 mode that panny might allow thru the "aspect ratio" button.
So, for you, you may rarely, if ever want to use it. So, why waste a button in your normal tv mode for that one. When you watch tv, generally you want the full 4:3 pix, and even rent or buy the "bigscreen" version of the dvd just to stay away from that 16:9 format. Well, crap, you want to watch a particular movie, but the video store only had the wide-screen version available, and it's saturday and you really want to watch it, and not mess with going back repeatedly till someone returns the big-screen version dvd.
Well, here's where you might want to use that rarely used function. Assign a small macro to do that "button press", but that "aspect" button was assigned to one of those phantom keys. You might think of other examples: i.e. you rarely use "random play" when you listed to cd's. You can assign that function to another of those phantom keys and access it thru another mini-macro.
The drawback is you can't directly access that function because it's on a button that doesn't actually exist.
Phantom keys would be especially handy on a remote like the 2116, where you can assign macros to the device buttons. If your panny tv has enough inputs where each video device has it's own input, and your receiver does likewise, then assigning those tv and receiver inputs to phantom keys and programming the device button macros would "totally" free-up the need for those on physical keys for your remote, laving more physical keys for other receiver functions, and possibly allow you to combine yout tv(with fewer needed buttons now), with something else, like maybe a simple vcr, with the basic functions of each.:)
Your 1994 can also probably be set up the same way, but the way the 2116 works, it's more ideally set-up for these. How to set them up will require a lot of thought and planning, but discrete access codes rather than multi-stepped toggle codes would make it a bit easier.
Jim