Wordpress Plugin Google Plus One w3c validator neutral

<?php
/*
Plugin Name: WP JS Plus One
Version: 1.0
Description: Adds Google's +1 button to posts using JavaScript
Author: konqi
Author URI: http://www.konqi.de
License: Public Domain
*/

/* Version Check */
    global $wp_version;
    $exit_msg='WP JS PlusOne This requires Wordpress 2.5 or newer.' .
        '<a href="http://codex.wordpress.org/Upgrading_Wordpress">Please update!</a>';

 if (version_compare($wp_version,"2.5","<"))
 {
    exit ($exit_msg);
 }

/* Adds the injection script to the Header of your Theme */
function wpjsplusonethis() {
    echo '<script type="text/javascript">
            <!--
            function replaceGooglePlusLinks(elementID, postLink)
            {
                targetElement = document.getElementById(elementID);

                if(targetElement != undefined && targetElement != null)
                {
                    targetElement.innerHTML = "<g:plusone size=\"small\" href=\"" + postLink +"\"></g:plusone>";
                    targetElement.setAttribute("style","display:inline;float:right;margin-left:1em;");
                }
            }
            -->
        </script>';
    echo '<script type="text/javascript" src="https://apis.google.com/js/plusone.js"></script>' . "\n";
}

function WPPlusOneThis_Link()
{
    global $post;
    global $googlejsplusonethis;

    // Insert place holder
    echo '<div id="googleplusone' . get_the_ID() . '"></div>' . "\n";

    // get the URL to the post or page
    $googlejsplusonethis .= 'replaceGooglePlusLinks("googleplusone' . get_the_ID() .'" , "'.get_permalink(get_the_ID()).'");' . "\n";
}

function wpjsplusonethisfooter()
{
    // write & execute replacement, let Google do the rest
    global $googlejsplusonethis;
    echo '<script type="text/javascript">
        <!--
            ' . $googlejsplusonethis . '
        -->
        </script>' . "\n";
}

function WPJWPlusOne_Filter($content)
{
    return $content.WPPlusOneThis_Link();
}

add_action('wp_head','wpjsplusonethis');
add_action('wp_footer','wpjsplusonethisfooter');

/* Show Google Plus One Link in content */
add_filter('the_content', 'WPJWPlusOne_Filter');
 ?>