The following intel document seems to have wrong information:
Intel 64 and IA-32 Architectures Software Developers Manual, Volume 1: Basic Architecture
Order Number: 253665-034US, March 2010
22.214.171.124 General-Purpose Registers in 64-Bit Mode
An instruction cannot reference legacy high-bytes (for example: AH, BH, CH, DH) and one of the
new byte registers at the same time (for example: the low byte of the RAX register).
Low byte of RAX is not a new byte register! Besides low byte of RAX is AL which can be used with AH at the same time. The "For example" clause above, seems wrong!!