    The following enumerations and types can be used by members of parser
classes generated by bic(). They are actually protected members inherited from
the parser's base class.
    itemization(
    it() bf(Base::ErrorRecovery__):nl()
        This enumeration defines two values:
        verb(
    DEFAULT_RECOVERY_MODE__,
    UNEXPECTED_TOKEN__
        )
       The tt(DEFAULT_RECOVERY_MODE__) terminates the parsing process. The
        non-default recovery procedure is available once an tt(error) token is
        used in a production rule. When the parsing process throws
        tt(UNEXPECTED_TOKEN__) the recovery procedure is started (i.e., it is
        started whenever a syntactic error is encountered or 
        tt(ERROR)tt(()) is called). 

        The recovery procedure consists of (1) looking for the first state on
        the state-stack having an error-production, followed by (2) handling
        all state transitions that are possible without retrieving a terminal
        token. Then, in the state requiring a terminal token and starting with
        the initial unexpected token (3) all subsequent terminal tokens are
        ignored until a token is retrieved which is a continuation token in
        that state. 

        If the error recovery procedure fails (i.e., if no acceptable token is
        ever encountered) error recovery falls back to the default recovery
        mode (i.e., the parsing process is terminated).

    it() bf(Base::Return__):nl()
        This enumeration defines two values:
        verb(
    PARSE_ACCEPT = 0,
    PARSE_ABORT = 1
        )
        (which are of course the tt(parse) function's return values).
     )
