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
"(?:)*" // same as the empty regex, the '*' accomplishes nothing
"(?:|x)*" // same as the empty regex, the alternative has no effect
"(?:x|)*" // same as 'x*', the empty alternative has no effect
"(?:x*|y*)*" // same as 'x*', the first alternative would always match, y* is never tried
"(?:x?)*" // same as 'x*'
"(?:x?)+" // same as 'x*'
Compliant solution
"x*"
