如何为Gravatar头像添加ALT属性

<?php echo get_avatar( $id_or_email, $size, $default, $alt, $args ); ?>

<?php echo get_avatar( $comment, 64 ); ?>

<?php echo get_avatar( $comment, 64, '', get_comment_author() ); ?>

wp_list_comments();

function mytheme_comment($comment, $args, $depth) {

    if ( 'div' === $args['style'] ) {

        $tag       = 'div';

        $add_below = 'comment';

    } else {

        $tag       = 'li';

        $add_below = 'div-comment';

    }

    ?>

    <<?php echo $tag ?> <?php comment_class( emptyempty( $args['has_children'] ) ? '' : 'parent' ) ?> id="comment-<?php comment_ID() ?>">

    <?php if ( 'div' != $args['style'] ) : ?>

        <div id="div-comment-<?php comment_ID() ?>" class="comment-body">

    <?php endif; ?>

    <div class="comment-author vcard">

        <?php if ( $args['avatar_size'] != 0 ) echo get_avatar( $comment, $args['avatar_size'] ); ?>

        <?php printf( __( '<cite class="fn">%s</cite> <span class="says">says:</span>' ), get_comment_author_link() ); ?>

    </div>

    <?php if ( $comment->comment_approved == '0' ) : ?>

         <em class="comment-awaiting-moderation"><?php _e( 'Your comment is awaiting moderation.' ); ?></em>

          <br />

    <?php endif; ?>

    <div class="comment-meta commentmetadata"><a href="<?php echo htmlspecialchars( get_comment_link( $comment->comment_ID ) ); ?>">

        <?php

        /* translators: 1: date, 2: time */

        printf( __('%1$s at %2$s'), get_comment_date(),  get_comment_time() ); ?></a><?php edit_comment_link( __( '(Edit)' ), '  ', '' );

        ?>

    </div>

    <?php comment_text(); ?>

    <div class="reply">

        <?php comment_reply_link( array_merge( $args, array( 'add_below' => $add_below, 'depth' => $depth, 'max_depth' => $args['max_depth'] ) ) ); ?>

    </div>

    <?php if ( 'div' != $args['style'] ) : ?>

    </div>

    <?php endif; ?>

    <?php

    }