That said, I'm having a specific bug. When mapping the "Tab" key to Spacebar+Shift, it doesn't work (rather, something is happening because instead of normally making a space when shifted, the spacebar does nothing. It seems to, however, act as Esc in vi and MicroB. When I mapped Tab to Up-Arrow+Fn, it works just fine.
key <SPCE> { [ space, at, Tab, bar ]}