What is the current thinking on best practices with regard to Plugins that use libraries that would often be installed with composer.

Obviously, in most cases one might be able to simply upload the vendors directory and load the init file or whatever the entry point is. But this is pretty messy.

I see that the square module uses spl_autoload_register( - I know nothing about spl :-)

Just interested to know if anyone has advice about best practices moving forward.