Miscellaneous non-critical issues may occur while Handler is being executed. The Handler will handle such issues by itself, thus no special handling is required for such cases. However, sometimes it's reasonable to be notified about such events. For this reason, the Handler exposes OnixS::SURF::MarketData::WarningListener
class and will invoke its OnixS::SURF::MarketData::WarningListener::onWarning
callback each time a non-critical issue will take place.