code: function(name, value, pos) {
  			// this is abstract implementation
  			var item = new EditElement(name, value);
  			this._children.push(item);
  			return item;
  		}
docs: Adds new attribute
  @param {String} name Property name
  @param {String} value Property value
  @param {Number} pos Position at which to insert new property. By
  default the property is inserted at the end of rule
  @returns {EditElement} Newly created element