-# %S = The letter 'S' or nothing (if a given value is exactly 1)
-# %W = A word (up to 10 characters)
-# %L = A word mapped to lower-case letters
-# %U = A word mapped to upper-case letters
-# %C = A word mapped to lower-case, first letter capitalised
-# %T = Several words of text, ending with a word of -1
-# %1 = A 1-digit number
-# %2 = A 2-digit number
-# ...
-# %9 = A 9-digit number
-# %B = Variable number of blanks
-# %! = The entire message should be suppressed