Validate a URL in PHP using a regular expression

// Copyright (c) 2010-2013 Diego Perini (http://www.iport.it) - MIT license
function isValidUrl($url)
{
    return 1 === preg_match('_^(?:(?:https?|ftp)://)(?:\S+(?::\S*)[email protected])?(?:(?!(?:10|127)(?:\.\d{1,3}){3})(?!(?:169\.254|192\.168)(?:\.\d{1,3}){2})(?!172\.(?:1[6-9]|2\d|3[0-1])(?:\.\d{1,3}){2})(?:[1-9]\d?|1\d\d|2[01]\d|22[0-3])(?:\.(?:1?\d{1,2}|2[0-4]\d|25[0-5])){2}(?:\.(?:[1-9]\d?|1\d\d|2[0-4]\d|25[0-4]))|(?:(?:[a-z\x{00a1}-\x{ffff}0-9]-*)*[a-z\x{00a1}-\x{ffff}0-9]+)(?:\.(?:[a-z\x{00a1}-\x{ffff}0-9]-*)*[a-z\x{00a1}-\x{ffff}0-9]+)*(?:\.(?:[a-z\x{00a1}-\x{ffff}]{2,}))\.?)(?::\d{2,5})?(?:[/?#]\S*)?$_iuS', $url);
}

$isUrl = isValidUrl('http://...');

$result = isValidUrl('http://example.org');
// $result = true
$result = isValidUrl('@example.org');
// $result = false