assets/js/vendor/backbone-relational.js
function( modelType ) {
			_.find( this._subModels, function( subModelDef ) {
				return _.find( subModelDef.subModels || [], function( subModelTypeName, typeValue ) {
					var subModelType = this.getObjectByName( subModelTypeName );

					if ( modelType === subModelType ) {
						// Set 'modelType' as a child of the found superModel
						subModelDef.superModelType._subModels[ typeValue ] = modelType;

						// Set '_superModel', '_subModelTypeValue', and '_subModelTypeAttribute' on 'modelType'.
						modelType._superModel = subModelDef.superModelType;
						modelType._subModelTypeValue = typeValue;
						modelType._subModelTypeAttribute = subModelDef.superModelType.prototype.subModelTypeAttribute;
						return true;
					}
				}, this );
			}, this );
		}
function( modelType ) {
			_.find( this._subModels, function( subModelDef ) {
				return _.find( subModelDef.subModels || [], function( subModelTypeName, typeValue ) {
					var subModelType = this.getObjectByName( subModelTypeName );

					if ( modelType === subModelType ) {
						// Set 'modelType' as a child of the found superModel
						subModelDef.superModelType._subModels[ typeValue ] = modelType;

						// Set '_superModel', '_subModelTypeValue', and '_subModelTypeAttribute' on 'modelType'.
						modelType._superModel = subModelDef.superModelType;
						modelType._subModelTypeValue = typeValue;
						modelType._subModelTypeAttribute = subModelDef.superModelType.prototype.subModelTypeAttribute;
						return true;
					}
				}, this );
			}, this );
		}
Check if the given modelType is registered as another model's subModel. If so, add it to the super model's
'_subModels', and set the modelType's '_superModel', '_subModelTypeName', and '_subModelTypeAttribute'.

@param {Backbone.RelationalModel} modelType