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*/
