+/**
+ * GtkThemingEngineClass:
+ * @parent_class: The parent class.
+ * @render_line: Renders a line between two points.
+ * @render_background: Renders the background area of a widget region.
+ * @render_frame: Renders the frame around a widget area.
+ * @render_frame_gap: Renders the frame around a widget area with a gap in it.
+ * @render_extension: Renders a extension to a box, usually a notebook tab.
+ * @render_check: Renders a checkmark, as in #GtkCheckButton.
+ * @render_option: Renders an option, as in #GtkRadioButton.
+ * @render_arrow: Renders an arrow pointing to a certain direction.
+ * @render_expander: Renders an element what will expose/expand part of
+ * the UI, as in #GtkExpander.
+ * @render_focus: Renders the focus indicator.
+ * @render_layout: Renders a #PangoLayout
+ * @render_slider: Renders a slider control, as in #GtkScale.
+ * @render_handle: Renders a handle to drag UI elements, as in #GtkPaned.
+ * @render_activity: Renders an area displaying activity, such as in #GtkSpinner,
+ * or #GtkProgressBar.
+ * @render_icon_pixbuf: Renders an icon as a #GdkPixbuf.
+ * @render_icon: Renders an icon given as a #GdkPixbuf.
+ *
+ * Base class for theming engines.
+ */
+struct _GtkThemingEngineClass