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<?php
/**
 * @link https://css-tricks.com/snippets/wordpress/insert-images-within-figure-element-from-media-uploader/
 */
function html5_insert_image( $html, $id, $caption, $title, $align, $url, $size, $alt ) {

    if ( current_theme_supports( 'html5' ) ) {

      $html = "<figure id='post-$id media-$id' class='align-$align'>";
      $html .= "<img src='$url' alt='$title' />";
      if ( $caption ) {
        $html .= "<figcaption>$caption</figcaption>";
      }
      $html .= "</figure>";
    }

    return $html;
}
add_filter( 'image_send_to_editor', 'html5_insert_image', 10, 8 );