function gallery_shortcode( $attr ) {
  $post = get_post();

  static $instance = 0;
  ++$instance;

  if ( ! empty( $attr['ids'] ) ) {
    // 'ids' is explicitly ordered, unless you specify otherwise.
    if ( empty( $attr['orderby'] ) ) {
      $attr['orderby'] = 'post__in';
    }
    $attr['include'] = $attr['ids'];
  }

  
/**
 * Filters the default gallery shortcode output.
 *
 * If the filtered output isn't empty, it will be used instead of generating
 * the default gallery template.
 *
 * @since 2.5.0
 * @since 4.2.0 The `$instance` parameter was added.
 *
 * @see gallery_shortcode()
 *
 * @param string $output   The gallery output. Default empty.
 * @param array  $attr     Attributes of the gallery shortcode.
 * @param int    $instance Unique numeric ID of this gallery shortcode instance.
 */
  $output = apply_filters( 'post_gallery', '', $attr, $instance );

  if ( ! empty( $output ) ) {
    return $output;
  }

  $html5 = current_theme_supports( 'html5', 'gallery' );
  $atts  = shortcode_atts(
    array(
      'order'      => 'ASC',
      'orderby'    => 'menu_order ID',
      'id'         => $post ? $post->ID : 0,
      'itemtag'    => $html5 ? 'figure' : 'dl',
      'icontag'    => $html5 ? 'div' : 'dt',
      'captiontag' => $html5 ? 'figcaption' : 'dd',
      'columns'    => 3,
      'size'       => 'thumbnail',
      'include'    => '',
      'exclude'    => '',
      'link'       => '',
    ),
    $attr,
    'gallery'
  );

  $id = (int) $atts['id'];

  if ( ! empty( $atts['include'] ) ) {
    $_attachments = get_posts(
      array(
        'include'        => $atts['include'],
        'post_status'    => 'inherit',
        'post_type'      => 'attachment',
        'post_mime_type' => 'image',
        'order'          => $atts['order'],
        'orderby'        => $atts['orderby'],
      )
    );

    $attachments = array();
    foreach ( $_attachments as $key => $val ) {
      $attachments[ $val->ID ] = $_attachments[ $key ];
    }
  } elseif ( ! empty( $atts['exclude'] ) ) {
    $post_parent_id = $id;
    $attachments = get_children(
      array(
        'post_parent'    => $id,
        'exclude'        => $atts['exclude'],
        'post_status'    => 'inherit',
        'post_type'      => 'attachment',
        'post_mime_type' => 'image',
        'order'          => $atts['order'],
        'orderby'        => $atts['orderby'],
      )
    );
  } else {
    $post_parent_id = $id;
    $attachments = get_children(
      array(
        'post_parent'    => $id,
        'post_status'    => 'inherit',
        'post_type'      => 'attachment',
        'post_mime_type' => 'image',
        'order'          => $atts['order'],
        'orderby'        => $atts['orderby'],
      )
    );
  }

  if ( ! empty( $post_parent_id ) ) {
    $post_parent = get_post( $post_parent_id );

    // terminate the shortcode execution if user cannot read the post or password-protected
    if (
    ( ! is_post_publicly_viewable( $post_parent->ID ) && ! current_user_can( 'read_post', $post_parent->ID ) )
    || post_password_required( $post_parent ) ) {
      return '';
    }
  }

  if ( empty( $attachments ) ) {
    return '';
  }

  if ( is_feed() ) {
    $output = "\n";
    foreach ( $attachments as $att_id => $attachment ) {
      if ( ! empty( $atts['link'] ) ) {
        if ( 'none' === $atts['link'] ) {
          $output .= wp_get_attachment_image( $att_id, $atts['size'], false, $attr );
        } else {
          $output .= wp_get_attachment_link( $att_id, $atts['size'], false );
        }
      } else {
        $output .= wp_get_attachment_link( $att_id, $atts['size'], true );
      }
      $output .= "\n";
    }
    return $output;
  }

  $itemtag    = tag_escape( $atts['itemtag'] );
  $captiontag = tag_escape( $atts['captiontag'] );
  $icontag    = tag_escape( $atts['icontag'] );
  $valid_tags = wp_kses_allowed_html( 'post' );
  if ( ! isset( $valid_tags[ $itemtag ] ) ) {
    $itemtag = 'dl';
  }
  if ( ! isset( $valid_tags[ $captiontag ] ) ) {
    $captiontag = 'dd';
  }
  if ( ! isset( $valid_tags[ $icontag ] ) ) {
    $icontag = 'dt';
  }

  $columns   = (int) $atts['columns'];
  $itemwidth = $columns > 0 ? floor( 100 / $columns ) : 100;
  $float     = is_rtl() ? 'right' : 'left';

  $selector = "gallery-{$instance}";

  $gallery_style = '';

  
/**
 * Filters whether to print default gallery styles.
 *
 * @since 3.1.0
 *
 * @param bool $print Whether to print default gallery styles.
 *                    Defaults to false if the theme supports HTML5 galleries.
 *                    Otherwise, defaults to true.
 */
  if ( apply_filters( 'use_default_gallery_style', ! $html5 ) ) {
    $type_attr = current_theme_supports( 'html5', 'style' ) ? '' : ' type="text/css"';

    $gallery_style = "
		<style{$type_attr}>
			#{$selector} {
				margin: auto;
			}
			#{$selector} .gallery-item {
				float: {$float};
				margin-top: 10px;
				text-align: center;
				width: {$itemwidth}%;
			}
			#{$selector} img {
				border: 2px solid #cfcfcf;
			}
			#{$selector} .gallery-caption {
				margin-left: 0;
			}
			/* see gallery_shortcode() in wp-includes/media.php */
		</style>\n\t\t";
  }

  $size_class  = sanitize_html_class( is_array( $atts['size'] ) ? implode( 'x', $atts['size'] ) : $atts['size'] );
  $gallery_div = "<div id='$selector' class='gallery galleryid-{$id} gallery-columns-{$columns} gallery-size-{$size_class}'>";

  
/**
 * Filters the default gallery shortcode CSS styles.
 *
 * @since 2.5.0
 *
 * @param string $gallery_style Default CSS styles and opening HTML div container
 *                              for the gallery shortcode output.
 */
  $output = apply_filters( 'gallery_style', $gallery_style . $gallery_div );

  $i = 0;

  foreach ( $attachments as $id => $attachment ) {

    $attr = ( trim( $attachment->post_excerpt ) ) ? array( 'aria-describedby' => "$selector-$id" ) : '';

    if ( ! empty( $atts['link'] ) && 'file' === $atts['link'] ) {
      $image_output = wp_get_attachment_link( $id, $atts['size'], false, false, false, $attr );
    } elseif ( ! empty( $atts['link'] ) && 'none' === $atts['link'] ) {
      $image_output = wp_get_attachment_image( $id, $atts['size'], false, $attr );
    } else {
      $image_output = wp_get_attachment_link( $id, $atts['size'], true, false, false, $attr );
    }

    $image_meta = wp_get_attachment_metadata( $id );

    $orientation = '';

    if ( isset( $image_meta['height'], $image_meta['width'] ) ) {
      $orientation = ( $image_meta['height'] > $image_meta['width'] ) ? 'portrait' : 'landscape';
    }

    $output .= "<{$itemtag} class='gallery-item'>";
    $output .= "
			<{$icontag} class='gallery-icon {$orientation}'>
				$image_output
			</{$icontag}>";

    if ( $captiontag && trim( $attachment->post_excerpt ) ) {
      $output .= "
				<{$captiontag} class='wp-caption-text gallery-caption' id='$selector-$id'>
				" . wptexturize( $attachment->post_excerpt ) . "
				</{$captiontag}>";
    }

    $output .= "</{$itemtag}>";

    if ( ! $html5 && $columns > 0 && 0 === ++$i % $columns ) {
      $output .= '<br style="clear: both" />';
    }
  }

  if ( ! $html5 && $columns > 0 && 0 !== $i % $columns ) {
    $output .= "
			<br style='clear: both' />";
  }

  $output .= "
		</div>\n";

  return $output;
}