Karabiner Elements
Complex Modifications (json)
- found in 
~/.config/karabiner/assets/complex_modifications 
From
- this field specifies the key combination that we want to press
 
To
- this field specifies the key combination that we want the system to understand
 
Modifiers
Mandatory
- this key must be pressed
 
Optional
- this key can be pressed and the mapping will be registered, though it is not necessary
 - ex. useful if say we have 
<Shift-Ctrl-j>mapped to "switch workspace", and we also don't care if we happen to also be holding downcmd. 
Tools
package.json has a pre/post version of every script