{"ast_node_type":"other","tokens":[{"end":78,"kind":"keyword","start":0,"text":"///"}]}
    /// be `mbe::TokenTree::Token`. No other variants are allowed. We store an
    /// This is only used for implicit token trees. The `mbe::TokenTree` *must*
    /// `mbe::TokenTree` rather than a `Token` so that `get()` can return a