the value at which the mark is placed, must be between the lower and upper limits of the scales’ adjustment
where to draw the mark. For a horizontal scale, #GTK_POS_TOP and %GTK_POS_LEFT are drawn above the scale, anything else below. For a vertical scale, #GTK_POS_LEFT and %GTK_POS_TOP are drawn to the left of the scale, anything else to the right.
Text to be shown at the mark, using [Pango markup]PangoMarkupFormat, or %NULL
2.16
Adds a mark at @value.
A mark is indicated visually by drawing a tick mark next to the scale, and GTK+ makes it easy for the user to position the scale exactly at the marks value.
If @markup is not %NULL, text is shown next to the tick mark.
To remove marks from a scale, use gtk_scale_clear_marks().