add note on default family names

Author: thomasp85

R/theme-elements.R

@@ -135,6 +135,10 @@ element_line <- function(colour = NULL, linewidth = NULL, linetype = NULL,
 #'   the graphics device being used for rendering the plot. See
 #'   [the systemfonts vignette](https://systemfonts.r-lib.org/articles/systemfonts.html)
 #'   for guidance on the best way to access fonts installed on your computer.
+#'   The values `"sans"`, `"serif"`, and `"mono"` should always be valid and
+#'   will select the default typeface for the respective styles. However, what
+#'   is considered default is dependant on the graphics device and the operating
+#'   system.
 #' @param face Font face ("plain", "italic", "bold", "bold.italic")
 #' @param hjust Horizontal justification (in \eqn{[0, 1]})
 #' @param vjust Vertical justification (in \eqn{[0, 1]})