38.1 Basic Concepts of Emacs Windows

A window in SXEmacs is the physical area of the screen in which a buffer is displayed. The term is also used to refer to a Lisp object that represents that screen area in SXEmacs Lisp. It should be clear from the context which is meant.

SXEmacs groups windows into frames. A frame represents an area of screen available for SXEmacs to use. Each frame always contains at least one window, but you can subdivide it vertically or horizontally into multiple nonoverlapping SXEmacs windows.

In each frame, at any time, one and only one window is designated as selected within the frame. The frame’s cursor appears in that window. At any time, one frame is the selected frame; and the window selected within that frame is the selected window. The selected window’s buffer is usually the current buffer (except when set-buffer has been used). See Current Buffer.

For practical purposes, a window exists only while it is displayed in a frame. Once removed from the frame, the window is effectively deleted and should not be used, even though there may still be references to it from other Lisp objects. Restoring a saved window configuration is the only way for a window no longer on the screen to come back to life. (See Deleting Windows.)

Each window has the following attributes:

• containing frame
• window height
• window width
• window edges with respect to the frame or screen
• the buffer it displays
• position within the buffer at the upper left of the window
• amount of horizontal scrolling, in columns
• point
• the mark
• how recently the window was selected

Users create multiple windows so they can look at several buffers at once. Lisp libraries use multiple windows for a variety of reasons, but most often to display related information. In Rmail, for example, you can move through a summary buffer in one window while the other window shows messages one at a time as they are reached.

The meaning of “window” in SXEmacs is similar to what it means in the context of general-purpose window systems such as X, but not identical. The X Window System places X windows on the screen; SXEmacs uses one or more X windows as frames, and subdivides them into SXEmacs windows. When you use SXEmacs on a character-only terminal, SXEmacs treats the whole terminal screen as one frame.

Most window systems support arbitrarily located overlapping windows. In contrast, SXEmacs windows are tiled; they never overlap, and together they fill the whole screen or frame. Because of the way in which SXEmacs creates new windows and resizes them, you can’t create every conceivable tiling of windows on an SXEmacs frame. See Splitting Windows, and Size of Window.

See Display, for information on how the contents of the window’s buffer are displayed in the window.

Function: windowp object

This function returns t if object is a window.