Improve wording (spotted by Lluis Revilla).

git-svn-id: https://svn.r-project.org/R/trunk@88121 00db46b3-68df-0310-9c12-caf00c1e9a41

Author: hornik

doc/manual/R-exts.texi

@@ -505,10 +505,10 @@ installed file: the convention is to use file @file{inst/COPYRIGHTS}.
 
 @c DESCRIPTION field Date
 The optional @samp{Date} field gives the @emph{release date} of the
-current version of the package.  It is strongly recommended@footnote{and
-required by @acronym{CRAN}, so checked by @command{R CMD check
---as-cran}.} to use the @samp{yyyy-mm-dd} format conforming to the ISO
-8601 standard.
+current version of the package.  Using the @samp{yyyy-mm-dd} format of
+the ISO 8601 standard is strongly recommended@footnote{and this format
+is required by @acronym{CRAN}, so checked by @command{R CMD check
+--as-cran} if a @samp{Date} is provided}.
 
 The @samp{Depends}, @samp{Imports}, @samp{Suggests}, @samp{Enhances},
 @samp{LinkingTo} and @samp{Additional_repositories} fields are discussed