I really don't understand how the "User: Data" field works. Couldn't find any documentation of this.
I want to set the Display format to "A certain key" to output the identifier value from this serialized data (relevant snippet):
When I enter identifier as key, I only get this notice and no output.
Notice: Undefined index: identifier in views_handler_field_serialized->render() (line 60 of www/htdocs/****/sites/all/modules/views/handlers/views_handler_field_serialized.inc).
What do I have to enter in the "Which key should be displayed" field exactly, to display the identifier value?