30.1 Gutter Intro

A gutter is a rectangle displayed along one edge of a frame. It can contain arbitrary text or graphics. It could be considered a generalization of a toolbar, although toolbars are not currently implemented using gutters.

In SXEmacs, a gutter can be displayed along any of the four edges of the frame, and two or more different edges can be displaying gutters simultaneously. The contents, thickness, and visibility of the gutters can be controlled separately, and the values can be per-buffer, per-frame, etc., using specifiers (see Specifiers).

Normally, there is one gutter displayed in a frame. Usually, this is the default gutter, containing buffer tabs, but modes cab override this and substitute their own gutter. This default gutter is usually positioned along the top of the frame, but this can be changed using set-default-gutter-position.

Note that, for each of the gutter properties (contents, thickness, and visibility), there is a separate specifier for each of the four gutter positions (top, bottom, left, and right), and an additional specifier for the “default” gutter, i.e. the gutter whose position is controlled by set-default-gutter-position. The way this works is that set-default-gutter-position arranges things so that the appropriate position-specific specifiers for the default position inherit from the corresponding default specifiers. That way, if the position-specific specifier does not give a value (which it usually doesn’t), then the value from the default specifier applies. If you want to control the default gutter, you just change the default specifiers, and everything works. A package such as VM that wants to put its own gutter in a different location from the default just sets the position-specific specifiers, and if the user sets the default gutter to the same position, it will just not be visible.