6c1a9dc58e
When a guest is created, the box metadata information is stored in the machine data directory. This allows modifications to happen to the Vagrantfile definition of the box in use (box name change, box version change, etc) while still allowing the Machine instance of an active guest successfully load the box currently backing it.
Vagrant Core Plugins
These are plugins that ship with Vagrant. Vagrant core uses its own plugin system to power a lot of the core pieces that ship with Vagrant. Each plugin will have its own README which explains its specific role.