adding an event listener to local buffer:
:au CursorHold <buffer>  echo 'hold'

event groups:
:augroup uncompress
:  au!
:  au BufEnter *.gz	%!gunzip
:augroup END


:au TextChanged <buffer> call ch_sendexpr(channel, 'changed')
:au TextChangedI <buffer> call ch_sendexpr(channel, 'changed_i')

":au TextChanged <buffer> call ch_sendexpr(channel, ['changed', 'x': col('.'), 'y': line('.')])
:au TextChanged <buffer> call ch_sendexpr(channel, ['changed', getpos('.')])
:au TextChangedI <buffer> call ch_sendexpr(channel, 'changed_i')


pseudocode for TextChanged diffing:

" not enough, maybe marks?
start_pos = min(last_pos, now_pos)
end_pos = max(last_pos, now_pos)