'Adds the given transformer to the block structure by recording
its current version number.'

def _add_transformer(self, transformer):

    if ((transformer.READ_VERSION == 0) or (transformer.WRITE_VERSION == 0)):
        raise TransformerException('Version    attributes    are    not    set    on    transformer    {0}.', transformer.name())
    self.set_transformer_data(transformer, TRANSFORMER_VERSION_KEY, transformer.WRITE_VERSION)
