duplicate group names should be okay without warning when defined over a union

[mfulton26]

MDN calls this out as valid in their valid cases:

/(?<firstName>\w+) (?<lastName>\w+)/;
/(?<year>\d{4})-\d{2}|\d{2}-(?<year>\d{4})/;

RegExr gives a warning though:

(?<year> ERROR: Duplicate group name.

\d Digit. Matches any digit character (0-9).

{4} Quantifier. Match 4 of the preceding token.

)  

https://regexr.com/89hjl

If the duplicate group name weren't defined over a union with a | then I would agree with the warning but over a union is safe and can be very helpful in validating & parsing strings (e.g. instruction names with different arguments following them).