Works in regex101
https://regex101.com/r/hAKpmr/1/
I tryied to use the pattern (?<=page=).*(?=&) in text: 'page=123&test=ok'
My code php:
preg_match('(?<=page=).*(?=&)', 'page=123&test=ok', $matches);
print_r($matches);
But had no matches and this warning: preg_match(): Unknown modifier '.'