How to use serialEvent ?

just took a look at the source of HardwareSerial

void serialEventRun(void)
{
#ifdef serialEvent_implemented
  if (Serial.available()) serialEvent();
#endif
#ifdef serialEvent1_implemented
  if (Serial1.available()) serialEvent1();
#endif
#ifdef serialEvent2_implemented
  if (Serial2.available()) serialEvent2();
#endif
#ifdef serialEvent3_implemented
  if (Serial3.available()) serialEvent3();
#endif
}

Apparently serialEvent is called for every received byte.
n yes, there doesnt seem to be any implementation of bufferUntil