Intercept keyboard on a specified program

[Paul Smith]

Dear All,

I am trying to intercept a program that I would specify so that I can
do something like: if I write, on the specified program,

br + TAB

expand that to "Best regards".

I know about AutoKey

https://github.com/autokey/autokey

but I would like to create my own, since AutoKey is a bit buggy.

Thanks in advance,

Paul