code: public function attach_media( $attachments, $iac_options, $item_ID ) {
  
  		if ( '1' !== $iac_options[ 'send_attachments' ] )
  			return $attachments;
  
  		$size  = 0;
  		$max_size = $iac_options[ 'attachment_max_size' ];
  		$links = array();
  		$files = array();
  		$dir   = wp_upload_dir();
  		$posts = get_children(
  			array(
  				'post_parent'    => $item_ID,
  				'post_type'      => 'attachment',
  				'post_status'    => array( 'publish', 'inherit' ),
  				'posts_per_page' => -1
  			)
  		);
  
  		$posts = apply_filters( 'iac_attach_media_posts', $posts, $item_ID, $iac_options );
  
  		if ( empty( $posts ) )
  			return $attachments;
  
  		$unique_posts = array();
  		foreach ( $posts as $p ) {
  			# avoid attach one file twice
  			if ( in_array( $p->ID, $unique_posts ) )
  				continue;
  			$meta = wp_get_attachment_metadata( $p->ID );
  			$file = self::get_thumbnail_file( $meta );
  			if ( ! $file )
  				$file = $dir[ 'basedir' ] . DIRECTORY_SEPARATOR . $meta[ 'file' ];
  
  			if ( ! file_exists( $file ) )
  				continue;
  
  			# limit the size of all attachments
  			$size = filesize( $file );
  			if ( $size < $max_size ) {
  				$attachments[]  = $file;
  				$unique_posts[] = $p->ID;
  			}
  		}
  
  		return $attachments;
  	}
docs: apply reference headers
  
  @param array $attachments
  @param array $iac_options
  @param int $post_ID
  @return array