
The FP8 formats have a "_" in the name so that they are: 1. Easier to read. 2. Possible to use in register expressions if/when they are supported. Some other bits do have defined meanings but they are not simple to name. Better that folks read the manual for those. See this page for the full details: https://developer.arm.com/documentation/ddi0601/2024-06/AArch64-Registers/FPMR--Floating-point-Mode-Register