Util.Debug, Util.Info, Util.Warn, Util.Error routines instead of
direct calls to console.*. Add "logging=XXX" query variable that sets
the logging level (default is "warn").
Logging values:
debug: code debug logging (many calls in performance path are also
commented for performance reasons).
info: informative messages including timing information.
warn: significant events
error: something has gone wrong
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