<chat_script>   ::= <script_cmd> | <chat_script> <script_cmd>
<script_cmd>    ::= <send_cmd> | <expect_cmd> | <echo_cmd> |
<read_cmd>
<send_cmd>      ::= "send" <quoted_string> | "send RETURN" | "send
BREAK"
<expect_cmd>    ::= "expect" <quoted_string> <number>
<expect_error>
<expect_error>  ::= "" | "onerror" <send_repeat>
<send_repeat>   ::= <send_cmd> <repeat> | <send_cmd> | <repeat>
<repeat>        ::= "repeat" <number> | "repeat"
<echo_cmd>      ::= "echo" <quoted_string>
<read_cmd>      ::= "read" <string>
<quoted_string> ::= "((<string>|<number>)[ ]*)+"
<string>        ::= ([a-zA-Z/_-&.%#@~+*\(){}$;:?><!]+[0-9"']*)+
<number>        ::= ([0-9,@*#$]*.)?[0-9,@*#$]+