clarification {object is not modified itself} and example revealing "additiveness"


git-svn-id: https://svn.r-project.org/R/trunk@66070 00db46b3-68df-0310-9c12-caf00c1e9a41
stepfun help touchup

git-svn-id: https://svn.r-project.org/R/trunk@66072 00db46b3-68df-0310-9c12-caf00c1e9a41
Avoid partial matching.


git-svn-id: https://svn.r-project.org/R/trunk@66073 00db46b3-68df-0310-9c12-caf00c1e9a41