This file is for the guest of this site only to jump into correct index page.
Some rental servers do not have file-type-name 'index.shtml' in DirectoryIndex,
and user should not add the file type 'shtml' in ".hcaccess" file.
If a host user wish to use SSI and let his guests be able to omit typing full file name (index.shtml) after domain name,
(i.e. type 'oebashi.clinic' instead for type full 'www.oebashi.clinic/index.shtml')
this file must be put in root directory,
not to be forced to jump into server's default index page.