Regular exp matching delimited string excepting trailing delimiters?

[Jeff Kowalczyk]

Can anyone suggest a reg exp (using re) that will match the entirety of a delimited string
of values, omitting zero or more delimiters at the end of the string? For example:

from 'A,B,C,123,D,E,,,,,,' with delimiter ',' match 'A,B,C,123,D,E'

I have (,*\Z) to match the trailing delimiters for removal with string slicing, but I'd
prefer to directly match the text to keep, or match both keep and discard as groups. What
would be the syntax for an omission like that? Thanks.