Zero length matches

Enter your regex: a?
Enter input string to search: 
I found the text "" starting at index 0 and ending at index 0.

Hace match porque ? hace match con CERO o un caracter.

Enter your regex: a*
Enter input string to search: 
I found the text "" starting at index 0 and ending at index 0.

Hace match porque * hace match con CERO o más caracteres.

A zero-length match can occur in several cases: in an empty input string, at the beginning of an input string, after the last character of an input string, or in between any two characters of an input string. Zero-length matches are easily identifiable because they always start and end at the same index position.

Un zero-length match siempre tienen una longitud de 0.