The `GtkSourceGutter` object represents the left or right gutter of the text view. It is used by [class@View] to draw the line numbers
and [class@Mark]s that might be present on a line. By packing additional [class@GutterRenderer] objects in the gutter, you can extend the
gutter with your own custom drawings.
To get a `GtkSourceGutter`, use the [[email protected]_gutter] function.
The gutter works very much the same way as cells rendered in a [[email protected]]. The concept is similar, with the exception that the
gutter does not have an underlying [[email protected]]. The builtin line number renderer is at position
gtk_source_view_gutter_position_lines (-30) and the marks renderer is at
gtk_source_view_gutter_position_marks (-20). The gutter sorts the renderers in ascending order, from left to right. So the marks
are displayed on the right of the line numbers.