How are multi vs single engine helicopters categorized? When looking at the FAA category, class, type list, you have airplane single-engine land, multi-engine land, etc. but just rotorcraft helicopter, gyrocopter, etc. 

How do I specify a multi vs single engine helicopter? Does the FAA differentiate, or are you able to fly a multi engine helicopter the day you get your helicopter certificate? 

For context, I'm making a web form where an operator can add their aircraft, and I want to be able to sort by single or multi engine helicopters because sometimes people request a multi engine helicopter. 

I ended up just doing this:
For the FAA, rotorcraft powered by more than one powerplant are not separately classified.

A random N-number search for a random twin-engine helicopter—AgustaWestland AW109—using the FAA registry yielded the type as: Rotorcraft.

However for a Boeing 707, the type came back as: Fixed Wing Multi-Engine.

I couldn't find a place where the different classes are listed on the FAA website, whether for fixed-wing or rotorcraft.