Pierre, I answered my own question shortly after I posted.
I did a search on google.com and it turns out that in some very fancy electronic dimmers (the ones where you have to press a rocker switch to control the lights), there is a tiny pull-tab switch underneath the faceplate.
By opening the switch you totally cut off current to the lightbulb. They call it an air-gap switch because that's what interrupts the flow of electricity -- a gap of air between the two contacts.
This was a PDF of installation instructions for some dimmer -- don't remember the brand, but I guess it will turn up if you do a search on "dimmer" and "air gap switch".
