tweak

git-svn-id: https://svn.r-project.org/R/trunk@66807 00db46b3-68df-0310-9c12-caf00c1e9a41
a few more details

git-svn-id: https://svn.r-project.org/R/trunk@66808 00db46b3-68df-0310-9c12-caf00c1e9a41
doc updates

git-svn-id: https://svn.r-project.org/R/trunk@66810 00db46b3-68df-0310-9c12-caf00c1e9a41