Headers
Headers represent the heading of a section of the document.
Headers should not be used to represent subheadings, subtitles, alternative titles or taglines unless these are intended represent the heading of a new section or subsection of the document.
In Markdown, headers can be defined in two ways: Setext headers and ATX headers.
Both header types represent the semantic meaning of the header in the same way, although ATX headers allow the writer to define additional heading levels.