The Marble Core Interface consists of the config, groups, behaviors, and items features. All Marble Contracts, at a minimum, must include the Marble Core Interface in order to be considered a valid Marble Digital Item contract.
Other additional plugin-like features, called Marble Layers, are optional and not required to be a valid Marble contract, but do add exceptional capabilities on top of the Marble Core Interface.
The Marble Config is a table in the contract that tracks administrative information like the contract name, version, admin, and serial counter.
Groups are sets of items that share behaviors and collective supply mechanics. The assigned group manager can also adjust group behaviors through standardized contract actions and is allowed to create new items within a group.
Items are the individual ownable objects stored in the contract. Every item created is given a unique contract-wide serial number that's used to identify it among all other items in the contract. Most Marble Layers add additional functionality on top of the base Items feature.