[Plugin: Events Manager] placeholder hook

hi,

i`m new to em…few days ago i made sum edits which worked…but i made them to the wrong files editing the core …so i try now to use the hooks and filters

i want to create a place holder for the recurrence_id

what`s wrong with that code?

<?php
//recurrence id placeholder

function my_em_styles_placeholders($replace, $EM_Event, $result){
 global $wp_query, $wp_rewrite;
 switch( $result ){
  case '#_RECURRENCEID':
      $replace = $this->recurrence_id;
  break;
 }
 return $replace;
}
add_filter('em_event_output_placeholder','my_em_styles_placeholders',1,3);
?>

thanks in advance

https://www.ads-software.com/extend/plugins/events-manager/