The documentation on the website is generated from the current code tree.
Current LXC git and the future LXC 2.1 will come with quite a number of the config keys renamed or removed which is what you’re seeing on the website.
It’s usually best to look at the manpage for the system you’re using LXC on “man lxc.container.conf” will show you the supported configuration keys for your system.
LXC 2.1 will be backward compatible with 2.0 but issue warnings about the renamed and deprecated configuration keys so you can update your config accordingly.