what is the difference between the two regex(negative lookaround)?

Question

i could match content between tr tags with this regex:

<tr\s+class='test'>((?!</tr>).)*</tr>

but if i put the star quantifiers inside the parenthesis right next to the dot metacharacters,they match only the whole pattern with capturing group empty.

$string = "<tr class='test'>
<td>test1</td>
</tr>
 <div class='ignored' >text text</div>
 <tr class='test'>
 <td>test2</td>
 </tr>";


preg_match_all("|<tr\s+class='test'>((?!</tr>).*)</tr>|si",$string,$matches);

print_r($matches);

i know what lookaround is but i'm not quite sure what exactly cause the difference. hope someone can shed some light on this. Thank you!

Answer 1

((?!</tr>).)*

The repetition is applied to ((?!</tr>).) and there is a single . and a single lookahead. Therefore, this will check each and every . (at each repetition) and make sure they are not followed by </tr>.

((?!</tr>).*)

This is actually (?!</tr>).* in disguise. There is a single lookahead and a single .*. The lookahead will check only the first ., but not the others, which is why everything will be matched, unless the immediate dots after the lookahead matches </tr>.