Validating the URL

Here I have wrote the recursive PCRE pattern for URL, hope you like it.

Recursive URL pattern features:
-------------------------------------------------------
1. Protocols https|http|ftp|ftps
2. WWW optional or only one.
3. Subdomain (unlimited) (Recursively match the subdomains) & (repeatedly - . at
    same time are not allowed).
4. domain only one (repeatedly - . at same time are not allowed).
5. extention only one mimimum 2, max five (repeatedly . at same time are not allowed).
6. End forward slash (/) is Optional.

<?php

/**
 * is_valid_url ()
 * Validate that given text is valid URL or not.
 *
 * @author   Junaid Atari <mj.atari@gmail.com>
 * @version  1.0
 * @param    string  $str    Text to validate.
 * @return   bool    TRUE on valid | FALSE on invalid.
 */
function is_valid_url ($str)
{
    //** Return if string not given or empty.
    if (!is_string ($str)
        || trim ($str) == '')
            return false;
   
    //** Recursive url pattern written by Junaid Atari.
    return preg_match ( '/^((http|ftp)(s?):\/\/)(www\.)?'.
                        '([a-z0-9]{1}([\-\.])?)*'.
                        '([a-z0-9]{1}([\-])?){1}'.
                        '(\.[a-z]{2,4})\/?$/i', $str ) == 0
        ? false
        : true;
}
/*
 +=======================================
 | Example
 +=======================================
*/
$urls = array (
    'http://www.yahoo.com/',
    'http://code.google.com',
    'https://login.live.com/',
    'http://my.name.is.domain.com.pk/',
    'https://www.name.is.2k-pcre.co.uk/',
);

foreach ($urls as $url)
    echo $url ." (" . (is_valid_url ($url)
                        ? 'Valid'
                        : 'Not valid') . ")<br />";
/*
 +=======================================
 | Output
 +=======================================
*/

/*
 http://www.yahoo.com/ (Valid)
 http://code.google.com (Valid)
 https://login.live.com/ (Valid)
 http://my.name.is.domain.com.pk/ (Valid)
 https://www.name.is.2k-pcre.co.uk/ (Valid)
*/