A regex should never include a repetitive pattern whose body would match the empty string. This is usually a sign that a part of the regex is
redundant or does not do what the author intended.
Noncompliant code example
r"(?:)*" # same as the empty regex, the '*' accomplishes nothing
r"(?:|x)*" # same as the empty regex, the alternative has no effect
r"(?:x|)*" # same as 'x*', the empty alternative has no effect
r"(?:x*|y*)*" # same as 'x*', the first alternative would always match, y* is never tried
r"(?:x?)*" # same as 'x*'
r"(?:x?)+" # same as 'x*'
Compliant solution
r"x*"
