Use make to only build new files in the documentation

Hello!
Chapter 5 of the ``FreeBSD Documentation Project Primer for New
Contributors'' shows how to build documentation:

 <https://docs.freebsd.org/en/books/fdp-primer/doc-build/>

I tried several consecutive times to run `make' for the
`documentation' (not the `website'), but each time it builds all
the files, even if none of them has been modified. The same with
`make build' (which populates `doc/documentation/public') and
`make run'.

My CPU is not that fast (it takes several minutes at each build). Is
there a way to build only the modified files, and not all the files,
each time?

Thank you anyway,

Rocky