Trait labels in std docs

Recently I noticed this: rustdoc apparently adds Read and Write labels at the top for types that implement std::io::Read and std::io::Write. Have I just not noticed this before, or is a somewhat new behavior? Regardless, I like it. It wouldn't have occurred to me to check if VecDeque<u8> implements Read and Write. As it so happens, I was going to create read and write wrappers for exactly this purpose when I noticed the labels on VecDeque. So how can I make use of these myself? I tried...