PIDAvailable is a Boolean property that indicates if a PID is available in the Text form of the Msg. 

Setting PIDAvailable to True will cause the PID value to be included in the text form of the Msg or setting this to false will remove the PID from the Text form of the Msg. A PID may not be included if it is not applicable to the computer or if the PID would be meaningless (e.g. the process by it's nature runs briefly such as SU). 

The value is obtained by parsing the TIdSysLogMsgPart.Text text property and setting this property will update the TIdSysLogMsgPart.Text property.

TIdSysLogMsgPart.PID 

TIdSysLogMsgPart.Text