diff --git a/src/library/base/man/paste.Rd b/src/library/base/man/paste.Rd
index 8ff68f6c80..31fc69af37 100644
--- a/src/library/base/man/paste.Rd
+++ b/src/library/base/man/paste.Rd
@@ -46,7 +46,8 @@ paste0(\dots,            collapse = NULL, recycle0 = FALSE)
   desirable, e.g.\sspace{}in \code{paste("the value of p is ", p)}.
 
   \code{paste0(\dots, collapse)} is equivalent to
-  \code{paste(\dots, sep = "", collapse)}, slightly more efficiently.
+  \code{paste(\dots, sep = "", collapse)}, slightly more efficiently
+  as it avoids handling a separator.
 
   If a value is specified for \code{collapse}, the values in the result
   are then concatenated into a single string, with the elements being
diff --git a/src/library/base/man/substr.Rd b/src/library/base/man/substr.Rd
index 973b19efb9..f332e6c269 100644
--- a/src/library/base/man/substr.Rd
+++ b/src/library/base/man/substr.Rd
@@ -98,6 +98,10 @@ substr("abcdef", 2, 4)
 substring("abcdef", 1:6, 1:6)
 ## strsplit() is more efficient ...
 
+## Extraction behavior from zero-length strings and empty strings
+substr(character(0), 1, 2)        # returns character(0)
+substring(c("abc", ""), 2)        # returns "bc" and ""
+
 substr(rep("abcdef", 4), 1:4, 4:5)
 x <- c("asfef", "qwerty", "yuiop[", "b", "stuff.blah.yech")
 substr(x, 2, 5)