{"ast_node_type":"other","tokens":[{"end":7,"kind":"keyword","start":0,"text":"///"}]}
    ///
    /// obligation. Hence we refine the `expr` "outwards-in" and bail at the first kind of expression/impl we don't recognize.
    /// This function returns a `Result<&Expr, &Expr>` - either way, it returns the `Expr` whose span should be