kernel config: COMPAT_FREEBSD4 ?

[Rob]

Hi,

The upcoming 5.3 stable kernel configuration has the option
COMPAT_FREEBSD4. What is the consequence of not having this
in the kernel?

If I install 5.3 from scratch on my system and compile all
software from scratch, will I run into trouble without the
option COMPAT_FREEBSD4 in the kernel?

Will I risk unexpected crashes, or do I get harmless
error messages in case option COMPAT_FREEBSD4 is needed
but not there?

What is the connection between this kernal option and
the port misc/compat4x ?

Rob.