Sets the the currently focused header bar. If @header_bar is %NULL, the decoration will be spread as if the header bars of the group were only one, otherwise @header_bar will be the only one to receive the decoration.
a #GtkHeaderBar of @self, or %NULL
See Implementation
Sets the the currently focused header bar. If @header_bar is %NULL, the decoration will be spread as if the header bars of the group were only one, otherwise @header_bar will be the only one to receive the decoration.