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38.13.2 Fringe Indicators

Fringe indicators are tiny icons displayed in the window fringe to indicate truncated or continued lines, buffer boundaries, etc.

— User Option: indicate-empty-lines

When this is non-nil, Emacs displays a special glyph in the fringe of each empty line at the end of the buffer, on graphical displays. See Fringes. This variable is automatically buffer-local in every buffer.

— User Option: indicate-buffer-boundaries

This buffer-local variable controls how the buffer boundaries and window scrolling are indicated in the window fringes.

Emacs can indicate the buffer boundaries—that is, the first and last line in the buffer—with angle icons when they appear on the screen. In addition, Emacs can display an up-arrow in the fringe to show that there is text above the screen, and a down-arrow to show there is text below the screen.

There are three kinds of basic values:

nil
Don't display any of these fringe icons.
left
Display the angle icons and arrows in the left fringe.
right
Display the angle icons and arrows in the right fringe.
any non-alist
Display the angle icons in the left fringe and don't display the arrows.

Otherwise the value should be an alist that specifies which fringe indicators to display and where. Each element of the alist should have the form (indicator . position). Here, indicator is one of top, bottom, up, down, and t (which covers all the icons not yet specified), while position is one of left, right and nil.

For example, ((top . left) (t . right)) places the top angle bitmap in left fringe, and the bottom angle bitmap as well as both arrow bitmaps in right fringe. To show the angle bitmaps in the left fringe, and no arrow bitmaps, use ((top . left) (bottom . left)).

— Variable: fringe-indicator-alist

This buffer-local variable specifies the mapping from logical fringe indicators to the actual bitmaps displayed in the window fringes. The value is an alist of elements (indicator . bitmaps), where indicator specifies a logical indicator type and bitmaps specifies the fringe bitmaps to use for that indicator.

Each indicator should be one of the following symbols:

truncation, continuation.
Used for truncation and continuation lines.
up, down, top, bottom, top-bottom
Used when indicate-buffer-boundaries is non-nil: up and down indicate a buffer boundary lying above or below the window edge; top and bottom indicate the topmost and bottommost buffer text line; and top-bottom indicates where there is just one line of text in the buffer.
empty-line
Used to indicate empty lines when indicate-empty-lines is non-nil.
overlay-arrow
Used for overlay arrows (see Overlay Arrow).

Each bitmaps value may be a list of symbols (left right [left1 right1]). The left and right symbols specify the bitmaps shown in the left and/or right fringe, for the specific indicator. left1 and right1 are specific to the bottom and top-bottom indicators, and are used to indicate that the last text line has no final newline. Alternatively, bitmaps may be a single symbol which is used in both left and right fringes.

See Fringe Bitmaps, for a list of standard bitmap symbols and how to define your own. In addition, nil represents the empty bitmap (i.e., an indicator that is not shown).

When fringe-indicator-alist has a buffer-local value, and there is no bitmap defined for a logical indicator, or the bitmap is t, the corresponding value from the default value of fringe-indicator-alist is used.