Smart Labels is a very useful feature from Gmail Labs that automatically categorizes messages. Right now, Gmail has categories for forum messages, social updates, notifications and promotions.
Gmail’s code includes some new smart labels for travel, receipts and events. I’ve tried to search for label:^smartlabel_event, label:^smartlabel_receipt, label:^smartlabel_travel and they don’t seem to work.
Google already categorizes your Gmail messages to enable the features added to Google Now a few months ago. Google needs to identify confirmation messages for restaurant reservations, hotel bookings, flights, events you purchased a ticket for, online orders and it’s obvious that Gmail could create smart labels for each category.