function expectCommaSeparator() {
        var token;

        if (extra.errors) {
            token = lookahead;
            if (token.type === Token.Punctuator && token.value === ',') {
                lex();
            } else if (token.type === Token.Punctuator && token.value === ';') {
                lex();
                tolerateUnexpectedToken(token);
            } else {
                tolerateUnexpectedToken(token, Messages.UnexpectedToken);
            }
        } else {
            expect(',');
        }
    }
@name expectCommaSeparator
@description Quietly expect a comma when in tolerant mode, otherwise delegates
to <code>expect(value)</code>
@since 2.0