Gtk.TextMark.prototype.set_visible

function set_visible(setting:Boolean):void {
    // Gjs wrapper for gtk_text_mark_set_visible()
}

Sets the visibility of mark; the insertion point is normally visible, i.e. you can see it as a vertical bar. Also, the text widget uses a visible mark to indicate where a drop will occur when dragging-and-dropping text. Most other marks are not visible. Marks are not visible by default.