WP Permalink Sanitizer

/**
 * Sanitizes title, replacing whitespace and a few other characters with dashes.
 *
 * Limits the output to alphanumeric characters, underscore (_) and dash (-).
 * Whitespace becomes a dash.
 *
 * @since 1.2.0
 *
 * @param string $title The title to be sanitized.
 * @param string $raw_title Optional. Not used.
 * @param string $context Optional. The operation for which the string is sanitized.
 * @return string The sanitized title.
 */
function sanitize_title_with_dashes($title, $raw_title = '', $context = 'display') {
    $title = strip_tags($title);
    // Preserve escaped octets.
    $title = preg_replace('|%([a-fA-F0-9][a-fA-F0-9])|', '---$1---', $title);
    // Remove percent signs that are not part of an octet.
    $title = str_replace('%', '', $title);
    // Restore octets.
    $title = preg_replace('|---([a-fA-F0-9][a-fA-F0-9])---|', '%$1', $title);

    if (seems_utf8($title)) {
            if (function_exists('mb_strtolower')) {
                    $title = mb_strtolower($title, 'UTF-8');
            }
            $title = utf8_uri_encode($title, 200);
    }

    $title = strtolower($title);
    $title = preg_replace('/&.+?;/', '', $title); // kill entities
    $title = str_replace('.', '-', $title);

    if ( 'save' == $context ) {
            // Convert nbsp, ndash and mdash to hyphens
            $title = str_replace( array( '%c2%a0', '%e2%80%93', '%e2%80%94' ), '-', $title );

            // Strip these characters entirely
            $title = str_replace( array(
                    // iexcl and iquest
                    '%c2%a1', '%c2%bf',
                    // angle quotes
                    '%c2%ab', '%c2%bb', '%e2%80%b9', '%e2%80%ba',
                    // curly quotes
                    '%e2%80%98', '%e2%80%99', '%e2%80%9c', '%e2%80%9d',
                    '%e2%80%9a', '%e2%80%9b', '%e2%80%9e', '%e2%80%9f',
                    // copy, reg, deg, hellip and trade
                    '%c2%a9', '%c2%ae', '%c2%b0', '%e2%80%a6', '%e2%84%a2',
            ), '', $title );

            // Convert times to x
            $title = str_replace( '%c3%97', 'x', $title );
    }

    $title = preg_replace('/[^%a-z0-9 _-]/', '', $title);
    $title = preg_replace('/\s+/', '-', $title);
    $title = preg_replace('|-+|', '-', $title);
    $title = trim($title, '-');

    return $title;
}