code: def init(req, model):
      
  
      rels = model.relationships
      params = req.get_param_as_list('include') or []
      params = [param.lower() for param in params]
  
      for param in params:
          _validate_no_nesting(param)
          _validate_rels(param, rels)
  
      return params
docs: Return an array of fields to include.