As discussed in “First Steps”, Ulysses uses special characters around text passages to let you define the meaning of these passages. This is called “markup”, and each distinct character set, such as underscores for emphasis, is called a “markup definition”. Any collection of definitions is then called a “markup language”. There are many markup languages in the wild, and you may have come across one or the other on message boards or blogging platforms: Textile, Setext, or the increasingly popular Markdown by John Gruber.
By default, Ulysses uses its native markup language, dubbed “Markdown XL”.