While talking about it with some other people, I realized that I don't remember EVER (with one exception; see below) seeing any of the three Lock keys being used with modifiers. Although the operating system will recognize the chords without issue, pressing Shift-Caps Lock, Ctrl-Caps Lock, Alt-Caps Lock (and any combination of the three mods) will ALL do the same as pressing Caps Lock without any mods at all; same for Num Lock and Scroll Lock...
... and I don't know of ANY operating system OR application where any combination of a lock key and modifiers is given any kind of meaning, unlike what happens with the other mod keys (think of Ctrl-F5, Alt-Shift-Tab, Ctrl-Esc, Shift-arrows, etc.). The ONE exception (that I know of) is the IBM Model M SSK, which maps Shift-Scroll Lock to be Num Lock.
I wonder if could this be taken advantage of in a more or less standardized manner. For example, compact keyboards (think 75% and under) have a limited amount of keys, and mapping all the Lock functions to a single key would be advantageous. We could make Caps Lock behave like this:
- Caps Lock: Caps Lock on/off.
- Shift-Caps Lock: Scroll Lock on/off.
- Ctrl-Caps Lock: Num Lock on/off.
- Alt-Caps Lock: turn on or off the Windows keys.