clean document

#' @inheritParams ggplot2::guide_axis

#' @param child a tibble of child axis information, see examples.

#' @param only_child if TRUE, will remove main axis elements.

#' @param child_size size of child axis label.

#' @param theme a ggplot theme object for child axis.

#' @rdname axis_child

#' @author Hou Yun

#' @export

guide_axis_child <- function(title = waiver(),

                             check.overlap = FALSE,

\item{only_child}{if TRUE, will remove main axis elements.}

\item{child_size}{size of child axis label.}

\item{theme}{a ggplot theme object for child axis.}

}

\description{

This function can be used to add children axis on a ggplot.

}

\author{

Hou Yun

}