def openerCheckToken(typebyte, size, opentype):
    """'typebyte' is the type of an incoming index token. 'size' is the
        value of header associated with this typebyte. 'opentype' is a list
        of open tokens that we've received so far, not including the one
        that this token hopes to create.

        This method should ask the current opener if this index token is
        acceptable, and is used in lieu of checkToken() when the receiver is
        in the index phase. Usually implemented by calling
        self.opener.openerCheckToken, thus delegating the question to the
        RootUnslicer.
        """
