diff --git a/Doc/lib/libstring.tex b/Doc/lib/libstring.tex
index 5f71ec8..b369901 100644
--- a/Doc/lib/libstring.tex
+++ b/Doc/lib/libstring.tex
@@ -235,17 +235,28 @@
   \function{joinfields()} was only used with two arguments.)
 \end{funcdesc}
 
-\begin{funcdesc}{lstrip}{s}
-  Return a copy of \var{s} but without leading whitespace characters.
+\begin{funcdesc}{lstrip}{s\optional{, chars}}
+Return a copy of the string with leading characters removed.  If
+\var{chars} is omitted or \code{None}, whitespace characters are
+removed.  If given and not \code{None}, \var{chars} must be a string;
+the characters in the string will be stripped from the beginning of
+the string this method is called on.
 \end{funcdesc}
 
-\begin{funcdesc}{rstrip}{s}
-  Return a copy of \var{s} but without trailing whitespace
-  characters.
+\begin{funcdesc}{rstrip}{s\optional{, chars}}
+Return a copy of the string with trailing characters removed.  If
+\var{chars} is omitted or \code{None}, whitespace characters are
+removed.  If given and not \code{None}, \var{chars} must be a string;
+the characters in the string will be stripped from the end of the
+string this method is called on.
 \end{funcdesc}
 
-\begin{funcdesc}{strip}{s}
-  Return a copy of \var{s} without leading or trailing whitespace.
+\begin{funcdesc}{strip}{s\optional{, chars}}
+Return a copy of the string with leading and trailing characters
+removed.  If \var{chars} is omitted or \code{None}, whitespace
+characters are removed.  If given and not \code{None}, \var{chars}
+must be a string; the characters in the string will be stripped from
+the both ends of the string this method is called on.
 \end{funcdesc}
 
 \begin{funcdesc}{swapcase}{s}