original_string: public static function get_mandatory_properties() {
          $properties = self::define_properties();
          $mandatoryproperties = array_filter($properties, function($property) {
              return empty($property['optional']);
          });
          return array_keys($mandatoryproperties);
      }
code: public static function get_mandatory_properties() {
          $properties = self::define_properties();
          $mandatoryproperties = array_filter($properties, function($property) {
              return empty($property['optional']);
          });
          return array_keys($mandatoryproperties);
      }
code_tokens: public static function get_mandatory_properties ( ) { $ properties = self :: define_properties ( ) ; $ mandatoryproperties = array_filter ( $ properties , function ( $ property ) { return empty ( $ property [ 'optional' ] ) ; } ) ; return array_keys ( $ mandatoryproperties ) ; }
docstring: The list of mandatory properties required on the question object to
  export.
  
  @return string[] List of properties.
docstring_tokens: The list of mandatory properties required on the question object to export .