ccepts nested paths. For example, to match single 
slice data in the example subjects directory, you can use 'Sub\w+; single\w+' 
regular expression where semi-colon is used as a delimiter. If there are no 
subject directories inside the input directory, leave it as empty.</li>

<li> session_dir_regexp - Regular expression used for getting the session 
directories inside the subject directories. Unlike subject_dir_regexp variable 
this cannot contain nested paths. If there are no session directories,