preg_replace for lazy-load

preg_replace-for-lazy-load.php

<?php

$content = '<img data-should-not-get-stripped src="https://example.com/example.jpg" alt="Not a real image." width="630" height="420">';
echo $content.PHP_EOL.str_repeat('-', 40).PHP_EOL;

$content = preg_replace(
  "/<img(?! (data-src|data-img-src|data-orig))([^']*?) src=\"([^']*?)\"([^']*?)>/", 
  '<img$2$1 data-img-src="$3" src="/r/1.2.3/t.gif'.'"$4>', 
  $content
);
echo $content.PHP_EOL.str_repeat('-', 40).PHP_EOL;

echo PHP_EOL.'data-should-not-get-stripped found?'.PHP_EOL;
echo strpos($content, 'data-should-not-get-stripped') !== false ? 'yes' : 'no';