Software Serial Research and Questions

SIGNAL(USART_RX_vect)
{
unsigned char c = UDR0;
store_char(c, &rx_buffer);
serialEvent();
}

Arguments/evidences are being built up why serialEvent() should be a SUR and not an ISR. Now, we are going to have our transmitted knowing (serialEvent() is a SUR) being elevated to intellectual knowledge (serialEvent() is indeed a SUR).

Thanks+.