code: function extend(data) {
  	return {
  		
  		uid   : typeof data.uid === 'string' ? data.uid : null,
  		title : data.title || 'Unnamed',
  		kind  : data.kind || 'fold',
  		value : data.value !== undefined ? data.value : null,
  		
  		isOpen  : ( !! data.isOpen ) || false,
  		subtree : data.subtree || [],
  		
  	};
  }
docs: /* exported resetModel