2.1 Window layout

2.1.1 Windows and panes

When the editor is called up an editor window is created and displayed (for those already familiar with Emacs running on a tty terminal, note that in this context a window is an object used by the window manager to display data, and not a term used to describe a portion of the editor display). The largest area of the editor window is taken up by an editor pane. Each window contains a single pane and therefore the term window is used throughout this manual as being synonymous with pane, unless more clarification is required.

Initially only one editor window is displayed. The corresponding editor pane is either blank (ready for text to be entered) or contains text from a file to be edited. The editor window displays text using the font associated with the editor pane.

2.1.2 Files and buffers

It is not technically correct to say that a window displays the contents of a file, rather that each window displays the contents of a buffer. A buffer is an object that contains data from the point of view of the editor, whereas a file contains data from the point of view of the operating system. A buffer is a temporary storage area used by the editor to hold the contents of a file while the process of editing is taking place. When editing has finished the contents of the buffer can then be written to the appropriate file. When the user exits from the editor, no information concerning buffers or windows is saved.

A buffer is often displayed in its own window, although it is also possible for many buffers to be associated with a single window, and for a single buffer to be displayed in more than one window.

In most cases, there is one buffer for each file that is accessed, but sometimes there is more than one buffer for a single file. There are also some buffers (such as the Echo Area, which is used to communicate with the user) that are not necessarily associated with any file.

2.1.3 The mode line

At the bottom of each editor window is a mode line that provides information concerning the buffer which that window is displaying. The contents of the mode line are as follows:

• "LATIN-1", "SJIS", "MACOS-ROMAN", "UTF-8" or "UNICODE", or other encoding name, indicating the encoding of any file associated with the buffer.
• "----" or "-**-" or "-%%-": the first indicates that the buffer is unchanged since it was last saved; the second that it has been changed; and the third that it is read only.
• the name of the buffer (the name of a buffer originating from a file is usually the same as the name of that file).
• the package of the current buffer written within braces.
• a major mode (such as Fundamental or Lisp). A buffer always operates in a single major mode.
• a minor mode (such as Abbrev or Auto-Fill). If no minor mode is in operation then this element is omitted from the mode line. An editor can operate in any number of minor modes.
• a position indicator showing the line numbers of the topmost and bottommost lines displayed in the window, and the total number of lines in the buffer. The editor can be changed to count characters rather than lines, and then displays percentages rather than line numbers.
• the pathname with which the buffer is associated.