The default template for Markdown notes is taken from /Hints/Preview/template, which is created by File ▸ Built In Hints. The note's $Text content looks like a template note—and is export template code—but it does not use any prototypes for styling and is not listed as a template as it is applied internally for use with Markdown-based preview. This allows the preview feature to work even if no export templates are currently defined.
The template automatically includes the CSS styles defined in the Preview style note.
The default template can be customised to add headers, footers, or other elements.