Markdown is a lightweight markup language for creating formatted text using a plain-text editor. John Gruber and Aaron Swartz created Markdown in 2004 as a markup language that is appealing to human readers in its source code form. Markdown is widely used in blogging, instant messaging, online forums, collaborative software, documentation pages, and readme files. The initial description of Markdown contained ambiguities and raised unanswered questions. To correct these problems, later implementations introduced subtle differences from the original version as well as syntax extensions. .Many developers choose to use 4-space or 2-space indentation. In MARKDOWN, each nested statement (e.g., a statement following a '{' brace) should be indented exactly once more than the previous line's indentation.)