It used to be that all you could see in a program for writing documents was the text itself, and to change the layout or font or margins, you had to write special “control codes,” or commands that would tell the computer that, for instance, “this part of the text should be in italics.”
That is in fact how for example LaTeX, Markdown and reStructuredText work and how some of us like to work with it. At least for me, it is liberating to be able to work directly with the plain and simple mark-up that exposes what is really going on instead of struggling with the sometimes endless frustration with trying to guess what Word seems to have misunderstood about how you want to format the text.