Fixes #4399

NEWS.md

@@ -87,6 +87,9 @@ precedence between `bins` and `binwidth`. (@eliocamp, #4651)
 
 * Key glyphs for `geom_boxplot()`, `geom_crossbar()`, `geom_pointrange()`, and
   `geom_linerange()` are now orientation-aware (@mjskay, #4732)
+
+* Updated documentation for `geom_smooth()` to more clearly describe effects of the 
+  `fullrange` parameter (@thoolihan, #4399).  
 
 # ggplot2 3.3.5
 This is a very small release focusing on fixing a couple of untenable issues 

R/stat-smooth.r

@@ -20,8 +20,9 @@
 #'   observations and `formula = y ~ s(x, bs = "cs")` otherwise.
 #' @param se Display confidence interval around smooth? (`TRUE` by default, see
 #'   `level` to control.)
-#' @param fullrange Should the fit span the full range of the plot, or just
-#'   the data?
+#' @param fullrange If `TRUE`, the smoothing line gets expanded to the range of the plot,
+#'   potentially beyond the data. This does not extend the line into any additional padding
+#'   created by `expansion`.
 #' @param level Level of confidence interval to use (0.95 by default).
 #' @param span Controls the amount of smoothing for the default loess smoother.
 #'   Smaller numbers produce wigglier lines, larger numbers produce smoother