class['level]event :'level #prioritizer -> 'level -> string ->object..end
The minimal class of diagnostic events. Use new event p v m to
construct an event object with the prioritizer p, the priority
level v, and the message m.
method prioritizer : 'level prioritizerReturns the prioritizer used to construct the object.
method level : 'levelReturns the priority level used to construct the object.
method message : stringReturns the message text used to construct the object.