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: spm_eeg_transform_cap.m
    path of file: ./repos/bspm/thirdparty/spm12/toolbox/MEEGtools
    
    the code of the file until where you have to start completion: function elec = spm_eeg_transform_cap(S)
% Transform an electrode cap to match the subject's headshape
% FORMAT shape = spm_eeg_transform_cap(S)
%
% S                    - input structure (optional)
% (optional) fields of S:
%   S.standard         - headshape (file) with the standard locations
%   S.custom           - headshape (file) with individually measured locations
%   S.outfile          - file name to save the output                     
%

    
function elec = spm_eeg_transform_cap(S)
% Transform an electrode cap to match the subject's headshape
% FORMAT shape = spm_eeg_transform_cap(S)
%
% S                    - input structure (optional)
% (optional) fields of S:
%   S.standard         - headshape (file) with the standard locations
%   S.custom           - headshape (file) with individually measured locations
%   S.outfile          - file name to save the output                     
%
% Output:
%   sens               - transformed sensors
%__________________________________________________________________________
% Copyright (C) 2008 Wellcome Trust Centre for Neuroimaging

% Vladimir Litvak
% $Id: spm_eeg_transform_cap.m 4020 2010-07-28 12:41:23Z vladimir $

SVNrev = '$Rev: 4020 $';

%-Startup
%--------------------------------------------------------------------------
spm('FnBanner', mfilename, SVNrev);
spm('FigName','Transform cap'); spm('Pointer','Watch');


%-Input
%--------------------------------------------------------------------------
if nargin == 0
    S = [];
end