[A-z0-9_] letters -> [A-z0-9_] symbols. Usually letters are characters of an alphabet, identifier characters are more often called as symbols. It is unusual to call digits as letters.
After both separators, a undercore symbol -> After both separators, an undercore symbol. It is better to use an before word starts with u letter.
[A-z0-9_] letters->[A-z0-9_] symbols. Usually letters are characters of an alphabet, identifier characters are more often called as symbols. It is unusual to call digits as letters.After both separators, a undercore symbol->After both separators, an undercore symbol. It is better to useanbefore word starts withuletter.