In order to specify the contents of a gutter, set one of the specifier
variables default-gutter, top-gutter,
bottom-gutter, left-gutter, or right-gutter.
These are specifiers, which means you set them with set-specifier
and query them with specifier-specs or specifier-instance.
You will get an error if you try to set them using setq. The
valid instantiators for these specifiers are gutter descriptors, as
described above. See Specifiers, for more information.
Most of the time, you will set default-gutter, which allows
the user to choose where the gutter should go.
The position of this gutter is specified in the function
default-gutter-position. If the corresponding position-specific gutter (e.g.top-gutterifdefault-gutter-positionistop) does not specify a gutter in a particular domain, then the value ofdefault-gutterin that domain, of any, will be used instead.
Note that the gutter at any particular position will not be displayed
unless its thickness (width or height, depending on orientation) is
non-zero and its visibility status is true. The thickness is controlled
by the specifiers top-gutter-height,
bottom-gutter-height, left-gutter-width, and
right-gutter-width, and the visibility status is controlled by
the specifiers top-gutter-visible-p,
bottom-gutter-visible-p, left-gutter-visible-p, and
right-gutter-visible-p (see Other Gutter Variables).
This function sets the position that the
default-gutterwill be displayed at. Valid positions are the symbolstop,bottom,leftandright. What this actually does is set the fallback specifier for the position-specific specifier corresponding to the given position todefault-gutter, and set the fallbacks for the other position-specific specifiers tonil. It also does the same thing for the position-specific thickness and visibility specifiers, which inherit from one ofdefault-gutter-heightordefault-gutter-width, and fromdefault-gutter-visible-p, respectively (see Other Gutter Variables).
This function returns the position that the
default-gutterwill be displayed at.
You can also explicitly set a gutter at a particular position. When
redisplay determines what to display at a particular position in a
particular domain (i.e. window), it first consults the position-specific
gutter. If that does not yield a gutter descriptor, the
default-gutter is consulted if default-gutter-position
indicates this position.
This function returns non-
nilif object is a gutter specifier. Gutter specifiers are the actual objects contained in the gutter variables described above, and their valid instantiators are gutter descriptors (see Gutter Descriptor Format).