On non-AMD64 flavours of FreeBSD, there is no manual page for boot
This manual page is only built for AMD64 architectures, and it is an alias for the actual boot_i386 manual page.
However, man boot is widely documented and learned behaviour, and there is no reason not to have a general manual page by this name.
So I wrote one from scratch: freebsd-boot.xml
This is result of converting the DocBook XML to HTML with xmlto.