documentation https://github.com/Nek5000/NekDoc/blob/9d76ef201cbe6448e30024699b6db3e5e59f3fdd/source/appendix.rst?plain=1#L94C1-L94C43 source code https://github.com/Nek5000/Nek5000/blob/11e94661faa8991b5c6e6711daf89d1cf1aa3ed5/core/prepost.f#L1053
