U.2 Top-Level Definitions, or Defuns

In Emacs, a major definition at the top level in the buffer is called a defun. The name comes from Lisp, but in Emacs we use it for all languages.

In most programming language modes, Emacs assumes that a defun is any pair of parentheses (or braces, if the language uses braces this way) that starts at the left margin. For example, in C, the body of a function definition is normally a defun, because the open-brace that begins it is normally at the left margin. A variable's initializer can also count as a defun, if the open-brace that begins the initializer is at the left margin.

However, some language modes provide their own code for recognizing defuns in a way that suits the language syntax and conventions better.

U.2.1 Left Margin Convention		An open-paren or similar opening delimiter starts a defun if it is at the left margin.
U.2.2 Moving by Defuns		Commands to move over or mark a major definition.
U.2.3 Imenu		Making buffer indexes as menus.
U.2.4 Which Function Mode		Which Function mode shows which function you are in.