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: ft_singleplotER.m
    path of file: ./repos/spm/external/fieldtrip
    
    the code of the file until where you have to start completion: function [cfg] = ft_singleplotER(cfg, varargin)

% FT_SINGLEPLOTER plots the event-related fields or potentials of a single
% channel or the average over multiple channels. Multiple datasets can be
% overlayed.
%
% Use as
%   ft_singleplotER(cfg, data)
% or
%   ft_singleplotER(cfg, data1, data2, ..., datan)
%
% The data can be an erp/erf produced by FT_TIMELOCKANALYSIS, a power
% spectrum or time-frequency respresentation produced by FT_FREQANALYSIS or 
% a connectivity spectrum produced by FT_CONNECTIVITYANALYSIS.
%
% The configuration can have the following parameters:
%   cfg.parameter     = field to be plotted on y-axis, for example 'avg', 'powspctrm' or 'cohspctrm' (default is automatic)
%   cfg.maskparameter = field in the first dataset to be used for masking of data; this is n
    
function
cfg = ft_checkconfig(cfg, 'forbidden',  {'channels', 'trial'}); % prevent accidental typos, see issue 1729
cfg = ft_checkconfig(cfg, 'unused',     {'cohtargetchannel'});
cfg = ft_checkconfig(cfg, 'renamedval', {'zlim', 'absmax', 'maxabs'});
cfg = ft_checkconfig(cfg, 'renamedval', {'directionality', 'feedforward', 'outflow'});
cfg = ft_checkconfig(cfg, 'renamedval', {'directionality', 'feedback',    'inflow'});
cfg = ft_checkconfig(cfg, 'renamed',    {'matrixside',     'directionality'});
cfg = ft_checkconfig(cfg, 'renamed',    {'channelindex',   'channel'});
cfg = ft_checkconfig(cfg, 'renamed',    {'channelname',    'channel'});
cfg = ft_checkconfig(cfg, 'renamed',    {'cohrefchannel',  'refchannel'});
cfg = ft_checkconfig(cfg, 'renamed',	  {'zparam',         'parameter'});
cfg = ft_checkconfig(cfg, 'renamed',    {'graphcolor',     'linecolor'});
cfg = ft_checkconfig(cfg, 'deprecated', {'xparam'});
cfg = ft_checkconfig(cfg, 'renamed',    {'newfigure',      'figure'});

% set the defaults
cfg.baseline        = ft_getopt(cfg, 'baseline',      'no');
cfg.trials          = ft_getopt(cfg, 'trials',        'all', 1);
cfg.xlim            = ft_getopt(cfg, 'xlim',          'maxmin');
cfg.ylim            = ft_getopt(cfg, 'ylim',          'maxmin');
cfg.zlim            = ft_getopt(cfg, 'zlim',          'maxmin');
cfg.comment         = ft_getopt(cfg, 'comment',        strcat([date '\n']));
cfg.axes            = ft_getopt(cfg, ' axes',         'yes');
cfg.fontsize        = ft_getopt(cfg, 'fontsize',       8);
cfg.interpreter     = ft_getopt(cfg, 'interpreter',   'none');  % none, tex or latex
cfg.hotkeys         = ft_getopt(cfg, 'hotkeys',       'yes');
cfg.interactive     = ft_getopt(cfg, 'interactive',   'yes');
cfg.maskparameter   = ft_getopt(cfg, 'maskparameter',  []);
cfg.colorgroups     = ft_getopt(cfg, 'colorgroups',   'condition'); % this is the only supported option
cfg.linecolor       = ft_getopt(cfg, 'linecolor',     []);
cfg.linestyle       = ft_getopt(cfg, 'linestyle',     '-');
cfg.linewidth       = ft_getopt(cfg, 'linewidth',      0.5);
cfg.maskstyle       = ft_getopt(cfg, 'maskstyle',     'box');
cfg.maskfacealpha   = ft_getopt(cfg, 'maskfacealpha', 1);
cfg.channel         = ft_getopt(cfg, 'channel',       'all');
cfg.title           = ft_getopt(cfg, 'title',          []);
cfg.directionality  = ft_getopt(cfg, 'directionality', []);
cfg.figurename      = ft_getopt(cfg, 'figurename',     []);
cfg.preproc         = ft_getopt(cfg, 'preproc',        []);
cfg.frequency       = ft_getopt(cfg, 'frequency',     'all'); % needed for frequency selection with TFR data
cfg.latency         = ft_getopt(cfg, 'latency',       'all'); % needed for latency selection with TFR data, FIXME, probably not used
cfg.showlegend