qmk-firmware/keyboards/uno/keymaps/default
..
keymap.c
readme.md

The default keymap for uno

Keymap

The 'Macro' key does a few things: If you open up textedit (was made for a mac), it sends "Command+n" for the first press to make a new document. It then types a few different messages, activates the RGB LED, and finally ends in a "scroll through the alphabet with a long press to confirm a certain character" keyboard mode.