Negative understanding of php regular expressions

Negative understanding of php regular expressions $ Str =' ';
$ Patten = '/<(?! AB) ([a-z] {9,})> /';
$ Str = preg_replace ($ patten, "", $ str );
Echo $ str;
Echo "\ n ";
$ Patten = '/<(?! AB) ([a-z] {8,})> /';
// Php regular expression positive and negative understanding
// Here it should be understood that there are at least eight characters between <> and it does not start with AB
// Incorrect understanding <> the first two characters cannot be AB and must be followed by at least 8 characters
$ Str = preg_replace ($ patten, "", $ str );
Echo $ str;
Echo "\ n ";
?>