2 indicates that the second pair of push|pop functions is
being used (differently numbered pairs won't interfere with each
other)
+ indicates that the layer is being "pushed" onto the
stack at some point, either when the key is pressed or when it is
released
- indicates that the layer is being "popped" off of the
stack at some point
the last 2 indicates the layer-number that will be
activated on "push".
See the project 'readme.md' file on the github page as a
starting point for learning more about how this firmware implements
layers.
Shifted keys are labeled with an sh at the beginning. This
indicates that a 'Shift' is generated with that keypress, the same as if you
had held down 'Shift', and pressed that key.
(null) indicates that no keypress or keyrelease will be
generated for that key, on that layer.
Blank keys indicate "transparency": if you press that key on that layer,
the key will act as if it was on whatever layer is active below the current
one.
Some keys may be labled with special functions (like
[btldr], which tells the Teensy to wait for the host to send it
a new firmware).