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: xmltree.m
    path of file: ./repos/cifti-matlab/ft_cifti/@xmltree
    
    the code of the file until where you have to start completion: function tree = xmltree(varargin)
% XMLTREE/XMLTREE Constructor of the XMLTree class
% FORMAT tree = xmltree(varargin)
% 
% varargin - XML filename or XML string
% tree     - XMLTree Object
%
%     tree = xmltree;             % creates a minimal XML tree: '<tag/>'
%     tree = xmltree('foo.xml');  % creates a tree from XML file 'foo.xml'
%     tree = xmltree('<tag>content</tag>') % creates a tree from string
%__________________________________________________________________________
%
% This is the constructor of the XMLTree class. 
% It creates a tree of an XML 1.0 file (after parsing) that is stored 
% using a Document Object Model (DOM) representation.
% See http://www.w3.org/TR/REC-xml for details about XML 1.0.
% See http://www.w3.org/DOM/ for details about DOM platform.
%__________________________________________________________________________
% Copyright (C) 2002-2011  http://www.artefact.tk/

% Guillaume Flandin
% $Id: xmltree.m 4460 2011-09-05 14:52:16Z guillaume $

    
function tree = xmltree(varargin)
% XMLTREE/XMLTREE Constructor of the XMLTree class
% FORMAT tree = xmltree(varargin)
% 
% varargin - XML filename or XML string
% tree     - XMLTree Object
%
%     tree = xmltree;             % creates a minimal XML tree: '<tag/>'
%     tree = xmltree('foo.xml');  % creates a tree from XML file 'foo.xml'
%     tree = xmltree('<tag>content</tag>') % creates a tree from string
%__________________________________________________________________________
%
% This is the constructor of the XMLTree class. 
% It creates a tree of an XML 1.0 file (after parsing) that is stored 
% using a Document Object Model (DOM) representation.
% See http://www.w3.org/TR/REC-xml for details about XML 1.0.
% See http://www.w3.org/DOM/ for details about DOM platform.
%__________________________________________________________________________
% Copyright (C) 2002-2011  http://www.artefact.tk/

% Guillaume Flandin
% $Id: xmltree.m 4460 2011-09-05 14:52:16Z guillaume $

switch(nargin)
    case 0
        tree.tree{1} = struct('type','element',...
                              'name','tag',...
                              'attributes',[],...
                              'contents',[],...
                              'parent',[],...
                              'uid',1);
        tree.filename = '';
        tree = class(tree,'xmltree');
    case 1
        if isa(varargin{1},'xmltree')
            tree = varargin{1};
        elseif ischar(varargin{1})
            % Input argument is an XML string
            if (~exist(varargin{1},'file') && ...
                ~isempty(xml_findstr(varargin{1},'<',1,1)))
                tree.tree = xml_parser(varargin{1});
                tree.filename = '';
            % Input argument is an XML filename
            else
                fid = fopen(varargin{1},'rt');
                if (fid == -1) 
                    error(['[XMLTree] Cannot open ' varargin{1}]);
                end