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: ImporterGroupSubjectST_MP_XLS.m
    path of file: ./repos/BRAPH-2/braph2/pipelines/structural multiplex
    
    the code of the file until where you have to start completion: classdef ImporterGroupSubjectST_MP_XLS < Importer
	%ImporterGroupSubjectST_MP_XLS imports a group of subjects with structural multiplex data from a series of XLS/XLSX files.
	% It is a subclass of <a href="matlab:help Importer">Importer</a>.
	%
	% ImporterGroupSubjectST_MP_XLS imports a group of subjects with structural 
	%  multiplex data from a series of XLS/XLSX files contained in a folder named 
	%  "GROUP_ID". All these files must be in the same folder; also, no other 
	%  files should be in the folder. Each file corresponds to a layer of the 
	%  multiplex and should be labeled with the layer number indicated as, e.g., 
	%  "GROUP_ID.1.xlsx" and "GROUP_ID.2.xlsx". 
	%  Each file contains the following columns: Subject ID (column 1), Subject 
	%  LABEL (column 2), Subject NOTES (column 3) and BrainRegions 
	%  (columns 4-end; one brain region value per column). The first row contains 
	%  the headers and each subsequent row the values for each subject.
	% The variables of interest are from another XLS/XLSX file named "GROUP_ID.vois.xlsx" 
	%  (if exisitng) consisting of the following columns: 
	%  Subject ID (column 1), covariates (subsequent c
    
function check_out = existsTag(tag)
			%EXISTSTAG checks whether tag exists in importer of ST MP subject group from XLS/XLSX/error.
			%
			% CHECK = ImporterGroupSubjectST_MP_XLS.EXISTSTAG(TAG) checks whether a property with tag TAG exists.
			%
			% Alternative forms to call this method are:
			%  CHECK = IM.EXISTSTAG(TAG) checks whether TAG exists for IM.
			%  CHECK = Element.EXISTSTAG(IM, TAG) checks whether TAG exists for IM.
			%  CHECK = Element.EXISTSTAG(ImporterGroupSubjectST_MP_XLS, TAG) checks whether TAG exists for ImporterGroupSubjectST_MP_XLS.
			%
			% Element.EXISTSTAG(TAG) throws an error if the TAG does NOT exist.
			%  Error id: [BRAPH2:ImporterGroupSubjectST_MP_XLS:WrongInput]
			%
			% Alternative forms to call this method are:
			%  IM.EXISTSTAG(TAG) throws error if TAG does NOT exist for IM.
			%   Error id: [BRAPH2:ImporterGroupSubjectST_MP_XLS:WrongInput]
			%  Element.EXISTSTAG(IM, TAG) throws error if TAG does NOT exist for IM.
			%   Error id: [BRAPH2:ImporterGroupSubjectST_MP_XLS:WrongInput]
			%  Element.EXISTSTAG(ImporterGroupSubjectST_MP_XLS, TAG) throws error if TAG does NOT exist for ImporterGroupSubjectST_MP_XLS.
			%   Error id: [BRAPH2:ImporterGroupSubjectST_MP_XLS:WrongInput]
			%
			% Note that the Element.EXISTSTAG(IM) and Element.EXISTSTAG('ImporterGroupSubjectST_MP_XLS')
			%  are less computationally efficient.
			%
			% See also getProps, existsTag.
			
			check = any(strcmp(tag, { 'ELCLASS'  'NAME'  'DESCRIPTION'  'TEMPLATE'  'ID'  'LABEL'  'NOTES'  'TOSTRING'  'WAITBAR'  'DIRECTORY'  'GET_DIR'  'BA'  'GR' })); %CET: Computational Efficiency Trick
			
			if nargout == 1
				check_out = check;
			elseif ~check
				error( ...
					['BRAPH2' ':ImporterGroupSubjectST_MP_XLS:' 'WrongInput'], ...
					['BRAPH2' ':ImporterGroupSubjectST_MP_XLS:' 'WrongInput' '\n' ...
					'The value ' tag ' is not a valid tag for ImporterGroupSubjectST_MP_XLS.'] ...
					)
			end