pitr question

Excuse the ignorance, but I see the following in the docs:

'In any case the hardware architecture must be the same — shipping from,
say, a 32-bit to a 64-bit system will not work.'

Is this specific to the hardware? That is to say, can I use pitr wal
shipping from 64 bit hardware to 64 bit hardware, where one machine is
running a 32 bit OS and the other is running a 64 bit OS?

Further:

Say 32 bit hardware and 64 bit hardware, where both are running a 32 bit OS?

Specifically speaking of RHEL.

Thanks.

--
Until later, Geoffrey

"I predict future happiness for America if they can prevent
the government from wasting the labors of the people under
the pretense of taking care of them."
- Thomas Jefferson