other words, you want to make it a shifted button, shifted by the GPIO 7
   button - you set it up with shiftMask and shiftBits both set to 0x0001,
   matching the shiftBits in the modifier button.
</p>
<pre>
   {
      buttons: [
         // ...earlier button entries go here...
         {
            shiftMask: 0x0001,   // make it sensitive to bit 0x0001
            shiftBits: 0x0001,   // operate only when bit 0x0001 is set -> GPIO 7 button is being pressed
            source: { type: "gpio", gp: 8 },
  