Can you use MBR with UEFI - a question about the UEFI specification

I am reading through the UEFI standard . On page 115, section 5 it discusses the GPT disk layout. I'm a bit confused as to exactly how this works. From the below, it sounds like UEFI will ignore the MBR. > A legacy MBR may be located at LBA 0 (i.e., the first logical block) > of the disk if it is not using the GPT disk layout (i.e., if it is > using the MBR disk layout). The boot code on the MBR is not executed > by UEFI firmware. So is this basically saying if you put the firmware in legacy boot mode, this is how to define an MBR which will play nicely with that legacy boot mode? Am I correct in saying that if the system's firmware were in UEFI mode, then a system with an MBR defined as specified in chapter 5 would not be bootable?