I don’t understand why this particular regex with PHP is failing:

]+)* href="([^"]+)"(\\s[^>]+)*>/i',
        function ($matches) {
                print_r($matches);
          return $matches[0];
        },
        'a'
);

When I run the code above, it echoes nothing to terminal.

But if I delete a single character from somewhere, sometimes the echo will work. For example, if change the word Martian to Martan (ie. drop the letter i), then everything works fine.

What have I misunderstood about my regex pattern? What is so special about the letter i that would break my regex?

However, this works fine in javascript:

'a'.match(/]+)* href="([^"]+)"(\s[^>]+)*>/i);

The javascript version gives me an array of matches.