You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: Panel.m
    path of file: ./repos/erplab/studio_functions/GUI Layout Toolbox/layout/+uix/+mixin
    
    the code of the file until where you have to start completion: classdef Panel < uix.mixin.Container
    %uix.mixin.Panel  Panel mixin
    %
    %  uix.mixin.Panel is a mixin class used by panels to provide various
    %  properties and template methods.
    
    %  Copyright 2009-2020 The MathWorks, Inc.
    
    properties( Access = public, Dependent, AbortSet )
        Selection % selected contents
    end
    
    properties( Access = protected )
        Selection_ = 0 % backing for Selection
    end
    
    properties( Access = protected )
        G1
    
function addChild( obj, child )
            
            % Check for bug
            if verLessThan( 'MATLAB', '8.5' ) && strcmp( child.Visible, 'off' )
                obj.G1218142 = true;
            end
            
            % Select new content
            oldSelection = obj.Selection_;
            newSelection = numel( obj.Contents_ ) + 1;
            obj.Selection_ = newSelection;
            
            % Call superclass method
            addChild@uix.mixin.Container( obj, child )
            
            % Show selected child
            obj.showSelection()
            
            % Notify selection change
            obj.notify( 'SelectionChanged', ...
                uix.SelectionData( oldSelection, newSelection ) )
            
        end