Form Object with simple DSL which allows nested Form Objects and arrays of Form Objects. Form Object is compatible with Rails form builders, can update its attributes from a hash and serialize them to a hash. Form Object attributes could be mapped to models attributes and Form Object can be loaded from and saved to models as well as serialized to a hash which reflects a model. ActiveModel::Errors could be copied from a model to Form Object.

TreeStruct allows to describe a structure with nested TreeStruct and with arrays of TreeStruct. The level of nesting is not limited.