parsing - how to check an ANTLR token is only used once or less in the parser -

In Anther, if I have a rule for example:

  Some rules: Token token;  

This will accept: "Token tokenb"

If I want to tip to be optional, then I can say,

  SomeRule: Tokna * Tokenb .;  

Then I could: "Tokna Tokenb" or "Tokenb" or "Tokna Tokai Token"

But this also means that it is repeated once again can go. Anyway, I can say that this token can be 1 or less but not more than one? Therefore it will accept:

"Token tokenb" or "tokenb" but "token token token"?

Many thanks

... anyway I can say Can this token be 1 or less but not more than one? ...

Here's how:

  Some rules: Token? Tokenb;  

Or:

Some rules: Token Tokenb. Tokenb;