I would say it is particularly true for Symfony, but other package maintainers, like Tailor Otwell for the Laravel framework, do an impressive job at documentin

I would say it is particularly true for Symfony, but other package maintainers, like Tailor Otwell for the Laravel framework, do an impressive job at documenting how to upgrade to newer versions and keeping BC to a minimum. For instance, I just recently upgraded from Symfony 2.7 to 2.8. The upgrade path was pretty much "Remove all deprecated warnings, upgrade your Symfony package, done". The same upgrade path is used from Symfony 2.8 to 3.0, which makes it really easy to upgrade. Symfony, as most PHP dependencies, can be installed via the "composer" package manager, which is pretty much the only package manager that is used in the PHP community, it seems. As dchesterton says, it is a very good piece of software.