I'm wondering if anyone knows of a precedent for a certain pattern
in a physical interface, such as a control panel or remote control.
The challenge is that a particular control panel design has multiple
states; in a given state, some functions are available while other
functions are unavailable. I'm considering a pattern in which each
button lights up when it's active/available and gets dark when it's
There are certainly many devices with buttons that light up in order
to reflect the on/off state of a particular feature (e.g.