Serial Port 1: Meaning of the "Com1/BMC" setting

[Richard Chan]

On a PE2850 what is the meaning of configuring 'Serial Port 1' to  
Com1/BMC (the alternatives being
Com1, BMC Serial, BMC NIC).

It is described helpfully (NOT) as:
BMC COM1 - "If enabled, makes BMC snoop the data stream going from the 
DB9 connector to COM 1."  Huh???

What is the use case of this particular setting? I gather for the other 
settings (please correct) it goes something like
Com1 (linux tty device talks via DB9 connector - use for normal serial IO)
BMC Serial (linux tty device and BMC share DB9 - use for normal serial 
IO/IPMI, toggle using escape keys)
BMC NIC (linux tty device talks via SOL - use to assess "serial port" 
using LAN)
...but...
BMC COM1 ????????????????????

Thanks
Richard