: Learning GNU Emacs, 3rd Edition

4.3 Working with Windows

Windows are areas on the screen in which Emacs displays the buffers that you are editing. You can have multiple windows on the screen at one time, each displaying a different buffer or different parts of the same buffer. Granted, the more windows you have, the smaller each one is; unlike GUI windows, Emacs windows can't overlap, so as you add more windows, the older ones shrink. The screen is like a pie; you can cut it into many pieces, but the more pieces you cut, the smaller they have to be. You can place windows side-by-side, one on top of the other, or mix them. Each window has its own mode line that identifies the buffer name, the modes you're running, and your position in the buffer. To make it clear where one window begins and another ends, mode lines are usually shaded.

As we've said, windows are not buffers. In fact, you can have more than one window on the same buffer. Doing so is often helpful if you want to look at different parts of a large file simultaneously. You can even have the same part of the buffer displayed in two windows, and any change you make in one window is reflected in the other.

The difference between buffers and windows becomes important when you think about marking, cutting, and pasting text. Marks are associated with buffers, not with windows, and each buffer can have only one mark. If you go to another window on the same buffer and set the mark, Emacs moves the mark to the new location, forgetting the place you set it last.

As for cursors, you have only one cursor, and the cursor's location determines the active window. However, although there is only one cursor at a time, each window does keep track of your current editing location separatelythat is, you can move the cursor from one window to another, do some editing, jump back to the first window, and be in the same place. A window's notion of your current position (whether or not the cursor is in the window) is called the point. Each window has its own point. It's easy to use the terms point and cursor interchangeablybut we'll try to be specific.

You can create horizontal windows or vertical windows or both, but personally we place vertical windows with the more advanced esoterica near the end of the chapter. Here we'll discuss creating horizontal windows, finding a file in a new window, and deleting windows.

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