What's the difference between these RegEx

Question

1. (\\d+|) vs (\\d+)?
2. [\\w\\W] vs [\\d\\D] vs .

Is there any difference between t

Answer 1

[\w\W] and [\d\D] are used in languages like JavaScript in which there isn't a dotall option. It matches all characters, including newlines, unlike . which matches everything but a newline.

   \w\W or \d\D   -> matches everything including newline characters
              .   -> matches everything except newline characters unless 
                     's' (dotall modifier) is specified 
(\d+|) or (\d+)?  -> matches 1 or more digits OR any position (null)
                     It could simply be written as '(\d*)'