On 2021-08-05 8:27 a.m., Peter Stephenson wrote:
d,1([^[:digit:]]*|)(N)
The (either_this|or_that) matches either what you originally said or nothing ("or_that" here is empty).
Marvelous, I know the logic of these regex things is very rigorous, so 
the 'not digit BUT still something'  construction must be handled and of 
course there will be a way of saying 'not digit but maybe nothing' too.  
Thanks Peter.  I tried to get the '|' working myself but didn't get it 
quite right.