SDF users can use Server Side Includes on their sites. Before the 2023 migration (to new hardware and NetBSD 9.3), SSI was enabled by default; now it must be enabled manually. To enable SSI in .shtml files, add the line below to the file .htaccess in your ~/html directory. Create the file if necessary.
AddHandler server-parsed .shtml
You may also need to add this line to make index.shtml your index page:
DirectoryIndex index.shtml