why do Vagrant docs suggest using public IP address for local VMs?

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http://serverfault.com – I'm following a tutorial to set up vagrant (a tool to build and configure portable virtual machine images), and it seems that vagrant documentation suggests using IPv4 address to configure a new box. That is a publicly routed IP adress, so I'm a bit confused why using this address is suggested. Since I don't own this network, I should not use an address from the range. Am I correct in thinking that I should only use either a public address from a network I own, or an address from one of the private ranges as defined in RFC 1918? If so, why does Vagrant documentation (HowTos)