The functions have the following meanings.
 
Function Meaning 
  A      All logical messages destined for and being displayed 
         on that terminal. 
  B      The logical message being displayed on that terminal 
         and all logical messages chained to it. 
  C      The current (level) logical message. 
  H      All logical messages chained to the base logical 
         message being displayed on that terminal. 
  R      All logical messages queued for immediate delivery 
(routed) to the terminal.