On
 Usage
• On[symbol::tag] switches on a message, so that it can be printed.
• On[s] switches on tracing for the symbol s.
• On[ ,  , ... ] switches on several messages.
• On[ ] switches on tracing for all symbols.
Notes
• When tracing is switched on, each evaluation of a symbol, on its own, or as a function, is printed, together with the result. • Note that the tracing information is printed when a function returns. As a result, traces of recursive functions appear in the opposite order from their calls. • On[s] is equivalent to On[s::trace]. • On[ ] is equivalent to On[s::trace] for all symbols. • New in Version 1.
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