What happens when Serial1 is directly connected to Serial2/3 on Mega 2560?

Projects Networking, Protocols, and Devices
10

I do not like talking to myself in public, but this works. It prints a 't' every second.

void setup()
{
  Serial.begin(9600);
  Serial1.begin(9600);
  Serial3.begin(9600);  
}

void loop()
{
  Serial1.write("t");
  delay(1000);
  Serial.write(Serial3.read());
}