Messages
The Wolfram Language uses its symbolic architecture to provide a convenient modular framework for generating and managing messages, both in programs and interactive sessions.
Quiet — evaluate an expression "quietly", outputting no messages
Off — globally switch off a message
On — switch on a message or a group of messages (some messages are off by default)
"Symbolics", "Graphics", "Compiler", ... — named groups of messages
Assert — give an assertion to be checked when code is executed
MessageName (::) — the symbolic name for a message, assigned with =
Message — output a named message, filling in specified elements
Check — check whether a message has been generated
CheckArguments — issue messages for functions with incorrect argument counts or options
Messages in Notebooks
MessageDialog — put up a message dialog
Why the Beep? ▪ Why the Coloring?
$MessagePrePrint — a function to apply to message arguments before printing
$MessageList ▪ MessageList ▪ MessagePacket
$Language — the default global language for messages
$MessageGroups — resettable lists of messages, mostly off by default
Failure Representation
$Failed ▪ $Aborted ▪ $TimedOut ▪ TerminatedEvaluation
Failure — symbolic representation of general failures
FailureQ ▪ Missing ▪ MissingQ ▪ DeleteMissing