Setting the kml_open attribute causes FME to write an <open> tag to the placemark, but I suspect it should be written to the folder the placemark is in. That would make it unsuitable to be a format attribute since it applies to all features in the placemark. I would argue it's better to make it a feature type property.
See https://knowledge.safe.com/questions/58958/how-do-you-specify-the-the-kml-open-attribute-to-f.html?&childToView;=59153#answer-59153 for additional discussion
