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: val2def.m
    path of file: ./repos/bspm/thirdparty/spm12/matlabbatch/@cfg_choice
    
    the code of the file until where you have to start completion: function [item, defaults] = val2def(item, defaults, funname, deftag)
% function [item, defaults] = val2def(item, defaults, funname, deftag)
% If a cfg_leaf item has a value, extract it and generate code for defaults
% retrieval. This function works in a way similar to harvest, but with a
% much simpler logic. Also, it modifies the returned configuration tree by
% clearing the .val fields if they are moved to defaults.
% Initially, defaults and deftag should be empty.
%
% This function is identical for cfg_branch and cfg_(m)choice classes.
%
% This code is part of a batch job configuration system for MATLAB. See 
%      help matlabbatch
% for a general overview.
%_______________________________________________________________________
% Copyright (C) 2007 Freiburg Brain Imaging

% Volkmar Glauche

    
function [item, defaults] = val2def(item, defaults, funname, deftag)
% function [item, defaults] = val2def(item, defaults, funname, deftag)
% If a cfg_leaf item has a value, extract it and generate code for defaults
% retrieval. This function works in a way similar to harvest, but with a
% much simpler logic. Also, it modifies the returned configuration tree by
% clearing the .val fields if they are moved to defaults.
% Initially, defaults and deftag should be empty.
%
% This function is identical for cfg_branch and cfg_(m)choice classes.
%
% This code is part of a batch job configuration system for MATLAB. See 
%      help matlabbatch
% for a general overview.
%_______________________________________________________________________
% Copyright (C) 2007 Freiburg Brain Imaging

% Volkmar Glauche
% $Id: val2def.m 5678 2013-10-11 14:58:04Z volkmar $

rev = '$Rev: 5678 $'; %#ok

csubs = substruct('.', treepart(item, true));
citems = subsref(item, csubs);
if ~isempty(deftag)
    deftag = [deftag '.'];
end