+@vindex YYLEX_PARAM
+If you wish to pass the additional parameter data to @code{yylex},
+define the macro @code{YYLEX_PARAM} just like @code{YYPARSE_PARAM}, as
+shown here:
+
+@example
+%@{
+struct parser_control
+@{
+ int nastiness;
+ int randomness;
+@};
+
+#define YYPARSE_PARAM parm
+#define YYLEX_PARAM parm
+%@}
+@end example
+
+You should then define @code{yylex} to accept one additional
+argument---the value of @code{parm}. (This makes either two or three
+arguments in total, depending on whether an argument of type
+@code{YYLTYPE} is passed.) You can declare the argument as a pointer to
+the proper object type, or you can declare it as @code{void *} and
+access the contents as shown above.
+