index.php

<?php namespace x\excerpt;

function page__content($content) {
    if (!$content) {
        return $content;
    }
    $exist = \strpos($content, "\f") ?: \strpos($content, '&#12;') ?: \stripos($content, '&#xc;');
    if (!$exist) {
        return $content;
    }
    // Normalize `&#12;` and `&#xc;` to a literal `\f`. Also, remove the surrounding HTML element if any (usually a paragraph element)
    return \preg_replace('/\s*<([\w:-]+)(?:\s[^>]*)?>\s*(?:[\f]|&#(?:12|x[cC]);)\s*<\/\1>\s*|\s*(?:[\f]|&#(?:12|x[cC]);)\s*/', "\f", $content);
}

function page__excerpt($excerpt) {
    // `excerpt` data has been set
    if ($excerpt) {
        return $excerpt; // Return the initial value
    }
    $content = $this->content ?? "";
    $exist = \strpos($content, "\f");
    // Page’s `content` is empty or excerpt marker does not exist, return the page’s `description`
    if (!$content || !$exist) {
        // If page’s `description` is empty, create a fake excerpt generated by the page’s `content`
        return '<p>' . ($this->description ?? \To::description((string) $content)) . '</p>';
    }
    $content = \trim(\substr($content, 0, $exist));
    return "" !== $content ? $content : null;
}

\Hook::set('page.content', __NAMESPACE__ . "\\page__content", 2.1);
\Hook::set('page.excerpt', __NAMESPACE__ . "\\page__excerpt", 2.1);