In the link, https://www.freebsd.org/doc/en_US.ISO8859-1/books/porters-handbook/makefile-masterdir.html

There is a old example with a link that leads to no where.
"japanese/xdvi300 also has all the regular patches, package files, etc. Running make there, it will take the default value for the resolution (300) and build the port normally."

When I click the "japanese/xdvi300", it leads to the error "404 Not Found".
Also, it seems that this example is no longer relevant so it needs to be updated with a newer example.