index.php

<?php namespace x\lazy;

function content($content) {
    if (!$content || (false === \strpos($content, '</iframe>') && false === \strpos($content, '<img'))) {
        return $content;
    }
    $r = "";
    foreach (\apart($content) as $v) {
        $n = \substr($v[0], 1, \strcspn($v[0], " \n\r\t", 1));
        if ('iframe' !== $n && 'img' !== $n) {
            $r .= $v[0];
            continue;
        }
        $t = new \HTML($v[0]);
        if (isset($t['loading']) || 0 === \strpos($t['src'] ?? "", 'data:image/')) {
            $r .= $v[0];
            continue;
        }
        $t['loading'] = 'lazy';
        $r .= $t;
    }
    return "" !== $r ? $r : null;
}

\Hook::set('content', __NAMESPACE__ . "\\content", 20);