a widget path describing a list of siblings. This path may not contain any siblings itself and it must not be modified afterwards.
index into @siblings for where the added element is positioned.
Return: the position where the element was inserted.
3.2
Appends a widget type with all its siblings to the widget hierarchy represented by @path. Using this function instead of gtk_widget_path_append_type() will allow the CSS theming to use sibling matches in selectors and apply :nth-child() pseudo classes. In turn, it requires a lot more care in widget implementations as widgets need to make sure to call gtk_widget_reset_style() on all involved widgets when the @siblings path changes.