Wordpress：如何为现有的Wordpress功能添加额外的HTML标签？

I am wondering how I can add a title="somecontent" tag to an existing Wordpress function.

Here is the code:

$author_id    = get_query_var( 'author' );
if(empty($author_id)) $author_id = get_the_author_meta('ID');
$alt          = get_the_author_meta('display_name');
$gravatar     = get_avatar( get_the_author_meta('email', $author_id), '81', '', $alt );
$name         = "<span class='author-box-name' ".avia_markup_helper(array('context' => 'author_name','echo'=>false)).">".get_the_author_meta('display_name', $author_id)."</span>";
$heading      = __("About",'avia_framework') ." ".$name;
$description  = get_the_author_meta('description', $author_id);

I would like to add the title tag specifically to:

$gravatar     = get_avatar( get_the_author_meta('email', $author_id), '81', '', $alt );

If you could point me at the method to do this it would be very helpful, thanks!

Untested, but this should get you started. In functions.php:

add_filter('get_avatar', 'add_avatar_attributes', 10, 5);
function add_avatar_attributes($avatar, $id_or_email, $size, $default, $alt){
    $doc= new DOMDocument();
    $doc->loadHTML($avatar);
    $img = $doc->getElementsByTagName('img')->item(0);
    $img->setAttribute("title", "somecontent");
    return $doc->saveHTML();
}