As mentioned for example [here](https://github.com/picmi-standard/picmi/blob/5a2594ad44ffbc67aa06944ece03f53018ce4027/PICMI_Python/particles.py#L25-L27) PICMI particle_type are supposed to be standardized in openPMD. However they are only standardized in the the upcoming openPMD 2.0 standard which isn't finalized yet. To avoid confusion this should be mentioned in PICMI.