docs: enumerate the eight dir codes in facet_wrap()

NEWS.md

@@ -36,6 +36,9 @@
 * `theme(strip.placement.x)` and `theme(strip.placement.y)` can be used for more
   granular control of strip placement when facetting. These have existed for some
   time but were not previously documented (@arcresu, #6827).
+* The `dir` argument of `facet_wrap()` is now documented with all
+  eight two-letter codes, clarifying their starting corner and fill
+  order (@CuiweiG, #6837).
 
 # ggplot2 4.0.2
 

R/facet-wrap.R

@@ -28,13 +28,24 @@ NULL
 #'   the plot. Using `strip.position` it is possible to place the labels on
 #'   either of the four sides by setting \code{strip.position = c("top",
 #'   "bottom", "left", "right")}
-#' @param dir Direction: either `"h"` for horizontal, the default, or `"v"`,
-#'   for vertical. When `"h"` or `"v"` will be combined with `as.table` to
-#'   set final layout. Alternatively, a combination of `"t"` (top) or
-#'   `"b"` (bottom) with `"l"` (left) or `"r"` (right) to set a layout directly.
-#'   These two letters give the starting position and the first letter gives
-#'   the growing direction. For example `"rt"` will place the first panel in
-#'   the top-right and starts filling in panels right-to-left.
+#' @param dir Direction in which panels are laid out. Must be one of
+#'   the following two-letter codes, where the first letter indicates
+#'   the initial fill direction and the pair identifies the starting
+#'   corner:
+#'
+#'   * `"lt"`: start in the top-left, fill left-to-right.
+#'   * `"tl"`: start in the top-left, fill top-to-bottom.
+#'   * `"lb"`: start in the bottom-left, fill left-to-right.
+#'   * `"bl"`: start in the bottom-left, fill bottom-to-top.
+#'   * `"rt"`: start in the top-right, fill right-to-left.
+#'   * `"tr"`: start in the top-right, fill top-to-bottom.
+#'   * `"rb"`: start in the bottom-right, fill right-to-left.
+#'   * `"br"`: start in the bottom-right, fill bottom-to-top.
+#'
+#'   Use `nrow` or `ncol` to control the shape of the grid; `dir`
+#'   controls the fill order within that shape. The shorthand values
+#'   `"h"` and `"v"` are superseded and retained only for backward
+#'   compatibility.
 #' @param axes Determines which axes will be drawn in case of fixed scales.
 #'   When `"margins"` (default), axes will be drawn at the exterior margins.
 #'   `"all_x"` and `"all_y"` will draw the respective axes at the interior