Google began testing booking appointments directly from the local search results box back in August. It looks like on Friday, December 4th, Google decided to release the developer documentation on how to add this structured markup to your page to add “Place Action rich snippets” to your site. This enables searchers to “place orders, make appointments and complete reservations.”
But despite it’s release on Friday, the documentation disappeared from the developer docs again, even though the links to the pages were still there. If you were to click on the link, the only thing you’d get in return is a “page not found status code. This happened before, back in late November when Google was prepping to release them.
Could the removal been intentional or an accident? The only one who knows is Google themselves.