Question

a* means zero or more of a.

In the string ‘abbabba’ we have two occurrence of abba. (abba)bba and abb(abba).
preg_match_all matches only first occurrence.

Am i missing any basic of regex fundamental?

$string = 'abbabba';

preg_match_all("/ab*a/", $string, $matches);

print_r($matches);

Array ( [0] => Array ( [0] => abba ) ) 

Answer 1

Searches subject for all matches to the regular expression given in pattern and puts them in matches in the order specified by flags.

After the first match is found, the subsequent searches are continued on from end of the last match.

Source