src/includes/classes/Core/Utils/Html.php
public function is(string $string, bool $strict = false): bool
    {
        if ($strict) {
            return mb_strpos($string, '</html>') !== false;
        }
        return mb_strpos($string, '<') !== false && preg_match('/\<[^<>]+\>/u', $string);
    }
public function is(string $string, bool $strict = false): bool
    {
        if ($strict) {
            return mb_strpos($string, '</html>') !== false;
        }
        return mb_strpos($string, '<') !== false && preg_match('/\<[^<>]+\>/u', $string);
    }
Is a string in HTML format?

@since 150424 Initial release.

@param string $string Any input string to test here.
@param bool   $strict Use strict (full DOM) check?

@return bool `TRUE` if string is HTML.