type does not already provide its own. In order to see backtraces, the
  `RUST_LIB_BACKTRACE=1` environment variable must be defined.

  type does not already provide its own. In order to see backtraces, they must
  be enabled through the environment variables described in [`std::backtrace`]:
  - If you want panics and errors to both have backtraces, set
    `RUST_BACKTRACE=1`;
  - If you want only errors to have backtraces, set `RUST_LIB_BACKTRACE=1`;
  - If you want only panics to have backtraces, set `RUST_BACKTRACE=1` and
    `RUST_LIB_BACKTRACE=0`.

  [`std::backtrace`]: https://doc.rust-lang.org/std/backtrace/index.html#environment-variables

    /// In order for the backtrace to be meaningful, the environment variable
    /// `RUST_LIB_BACKTRACE=1` must be defined. Backtraces are somewhat

    /// In order for the backtrace to be meaningful, one of the two environment
    /// variables `RUST_LIB_BACKTRACE=1` or `RUST_BACKTRACE=1` must be defined
    /// and `RUST_LIB_BACKTRACE` must not be `0`. Backtraces are somewhat

    ///
    /// - If you want panics and errors to both have backtraces, set
    ///   `RUST_BACKTRACE=1`;
    /// - If you want only errors to have backtraces, set
    ///   `RUST_LIB_BACKTRACE=1`;
    /// - If you want only panics to have backtraces, set `RUST_BACKTRACE=1` and
    ///   `RUST_LIB_BACKTRACE=0`.

//!   type does not already provide its own. In order to see backtraces, the
//!   `RUST_LIB_BACKTRACE=1` environment variable must be defined.

//!   type does not already provide its own. In order to see backtraces, they
//!   must be enabled through the environment variables described in
//!   [`std::backtrace`]:
//!
//!   - If you want panics and errors to both have backtraces, set
//!     `RUST_BACKTRACE=1`;
//!   - If you want only errors to have backtraces, set `RUST_LIB_BACKTRACE=1`;
//!   - If you want only panics to have backtraces, set `RUST_BACKTRACE=1` and
//!     `RUST_LIB_BACKTRACE=0`.

//!   [`std::backtrace`]: https://doc.rust-lang.org/std/backtrace/index.html#environment-variables
//!