clarify the second argument in autoplot RGLab/flowWorkspace#248

R/autoplot.R

@@ -2,9 +2,10 @@
 #'
 #' Overloaded autoplot for the cytomertry data structure: flowFrame or flowSet, Gatinghierarchy, GatingSet.
 #' It plots the cytometry data with geom_histogram, geom_density or geom_hex.
+#' When autoplot a GatingSet/Gatinghierarchy, the second argument should be a gate or population node. And the dimensions(channels/markers) are deduced from the gate dimensions.
 #'
 #' @param object flowFrame, flowSet, GatingSet object
-#' @param x define the x dimension of the plot. When object is a flowFrame, it can be missing, which plots 1d density plot on all the channels. 
+#' @param x define the x dimension of the plot (not used when object is a GatingSet). When object is a flowFrame, it can be missing, which plots 1d density plot on all the channels. 
 #' @param y define the y dimension of the plot. Default is NULL, which means 1d densityplot.
 #' @param bins passed to geom_hex
 #' @param axis_inverse_trans logical flag indicating whether to add \link{axis_x_inverse_trans} and axis_x_inverse_trans layers.