not expand main plot

  ## init and add panel grid

  p <- hyplot(df) +

    geom_panel_grid(colour = grid_col, size = grid_size) +

    ggplot2::coord_fixed() +

    ggplot2::coord_fixed(expand = FALSE) +

    theme(panel.background = element_blank())

  ## add child axis

  if (isTRUE(axis_child)) {

    p <- p

  }

  class(p) <- c("qpairs", class(p))

  p

}