{"ast_node_type":"other","tokens":[{"end":85,"kind":"keyword","start":0,"text":"///"}]}
    ///   provided `span` and `key` through [`DiagCtxtHandle::steal_non_err()`]. This
    /// - Level::Warning and lower (i.e. !is_error()): can be accessed with the
    ///   allows cancelling and downgrading of the diagnostic. Returns `None`.