system/classes/Model.php
public function isPlaceholder($attributeName)
    {
      // Ref this model's attributes in a shorter variable.
      $def = $this->model_attributes[$attributeName];

      if (isset($def['models']) || (isset($def['model']) && isset($def['usesRefTable']))) {
        return true;
      }
      return false;
    }
public function isPlaceholder($attributeName)
    {
      // Ref this model's attributes in a shorter variable.
      $def = $this->model_attributes[$attributeName];

      if (isset($def['models']) || (isset($def['model']) && isset($def['usesRefTable']))) {
        return true;
      }
      return false;
    }
Sometimes a placeholder value of "1" will be loaded into models which indicate the data is available,
but must be fetched if needed. This method indicates whether or not a value of 1 means it's a placeholder.

@param $attributeName string An attribute name who's value in model_data is "1"
@return bool