   The valid command characters are:
	B - Backup, type the previous message
	C - Current message, give current message number and the file name
	D - Delete, mark a message sequence for deletion
	E - Exit, exit and update the open file
	G - Goto, changes the current message number
	H - Headers, print the headers of a message sequence
	L - List, provide a listing of a message sequence
	M - Move, move a sequence into another file and then delete it
	N - Next, type the next message
	O - Overwrite, remove all deleted messages from the file
	P - Put, move a message sequence into another file
	Q - Quit, leave the msg program
	R - Read, open and read another file
	T - Type, output a message sequence to the console
	U - Undelete, remove the deletion mark from a message sequence
	Single quote(') - Mark a message sequence as 'examined'
	Minus sign(-) - Mark a message sequence as 'not examined'

   A message sequence is composed of:
	1) any single number or 
	2) any two numbers separated by any nonnumeric character or
	3) one of the following special sequence characters:
		A - All messages
		D - Deleted messages
		E - Examined messages
		I - All messages in inverse order
		N - Not examined messages
		U - Undeleted messages
