new layer for F1-F12 and bootldr
layer 2 above shift, new F-Layer above alt, layer 3 where layer 2 was

- because it is very common to alternate between shifted keys and layer 2
- to enable alt+F4 et al to be pressed with one hand
layer 2 on left thumb next to shift, enter on right index finger

space for testing purposes also on left index finger

page up and down where home and end have been.
don't know where to put home and end, maybe just use the ones from layer 3
tab and enter on layer 4