org.texi: New example on babel :post header

* org.texi (post): Clarification and new example.

doc/org.texi

@@ -15987,10 +15987,11 @@ code block execution.  When a post argument is given, the results of the code
 block will temporarily be bound to the @code{*this*} variable.  This variable
 may then be included in header argument forms such as those used in @ref{var}
 header argument specifications allowing passing of results to other code
-blocks, or direct execution via Emacs Lisp.
+blocks, or direct execution via Emacs Lisp.  Additional header arguments may
+be passed to the @code{:post}-function.
 
-The following example illustrates the usage of the @code{:post} header
-argument.
+The following two examples illustrate the usage of the @code{:post} header
+argument.  The first example shows how to attach a attribute-line via @code{:post}.
 
 @example
 #+name: attr_wrap
@@ -16015,6 +16016,31 @@ argument.
 :END:
 @end example
 
+The second examples shows how to use @code{:post} together with the
+@code{:colnames} header argument.
+@example
+#+name: round-tbl
+#+begin_src emacs-lisp :var tbl="" fmt="%.3f"
+  (mapcar (lambda (row)
+            (mapcar (lambda (cell)
+                      (if (numberp cell)
+                          (format fmt cell)
+                        cell))
+                    row))
+          tbl)
+#+end_src
+
+#+begin_src R :colnames yes :post round-tbl[:colnames yes](*this*)
+set.seed(42)
+data.frame(foo=rnorm(1))
+#+end_src
+
+#+RESULTS:
+|   foo |
+|-------|
+| 1.371 |
+@end example
+
 @node prologue
 @subsubsection @code{:prologue}
 @cindex @code{:prologue}, src header argument