From reading the source, it turns out that the setkey() method can

take an optional string key, but if key is not given, the method does
nothing!  In the rewrite (see upcoming check-in), I left things this
way, but here I document that this is the case.

Doc/lib/librotor.tex

@@ -35,8 +35,9 @@ if it is omitted, a default value of 6 will be used.
 Rotor objects have the following methods:
 
 \renewcommand{\indexsubitem}{(rotor method)}
-\begin{funcdesc}{setkey}{}
-Reset the rotor to its initial state.
+\begin{funcdesc}{setkey}{\optional{key}}
+Sets the rotor's key to \var{key}.  If \var{key} is not given, this
+function does nothing\footnote{This is for backwards compatibility.}.
 \end{funcdesc}
 
 \begin{funcdesc}{encrypt}{plaintext}

Doc/librotor.tex

@@ -35,8 +35,9 @@ if it is omitted, a default value of 6 will be used.
 Rotor objects have the following methods:
 
 \renewcommand{\indexsubitem}{(rotor method)}
-\begin{funcdesc}{setkey}{}
-Reset the rotor to its initial state.
+\begin{funcdesc}{setkey}{\optional{key}}
+Sets the rotor's key to \var{key}.  If \var{key} is not given, this
+function does nothing\footnote{This is for backwards compatibility.}.
 \end{funcdesc}
 
 \begin{funcdesc}{encrypt}{plaintext}