Sets whether @child should appear in a secondary group of children.
A typical use of a secondary child is the help button in a dialog.
This group appears after the other children if the style
is %GTK_BUTTONBOX_START, %GTK_BUTTONBOX_SPREAD or
%GTK_BUTTONBOX_EDGE, and before the other children if the style
is %GTK_BUTTONBOX_END. For horizontal button boxes, the definition
of before/after depends on direction of the widget (see
gtk_widget_set_direction()). If the style is %GTK_BUTTONBOX_START
or %GTK_BUTTONBOX_END, then the secondary children are aligned at
the other end of the button box from the main children. For the
other styles, they appear immediately next to the main children.
Sets whether @child should appear in a secondary group of children. A typical use of a secondary child is the help button in a dialog.
This group appears after the other children if the style is %GTK_BUTTONBOX_START, %GTK_BUTTONBOX_SPREAD or %GTK_BUTTONBOX_EDGE, and before the other children if the style is %GTK_BUTTONBOX_END. For horizontal button boxes, the definition of before/after depends on direction of the widget (see gtk_widget_set_direction()). If the style is %GTK_BUTTONBOX_START or %GTK_BUTTONBOX_END, then the secondary children are aligned at the other end of the button box from the main children. For the other styles, they appear immediately next to the main children.