///
    /// The primary reason to use `error.context(...)` instead of
    /// `result.context(...)` via the `Context` trait would be if the context
    /// needs to depend on some data held by the underlying error:
    ///
    /// ```
    /// # use std::fmt::{self, Debug, Display};
    /// #
    /// # type T = ();
    /// #
    /// # impl std::error::Error for ParseError {}
    /// # impl Debug for ParseError {
    /// #     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
    /// #         unimplemented!()
    /// #     }
    /// # }
    /// # impl Display for ParseError {
    /// #     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
    /// #         unimplemented!()
    /// #     }
    /// # }
    /// #
    /// use std::fs::File;
    /// use std::path::Path;
    ///
    /// struct ParseError {
    ///     line: usize,
    ///     column: usize,
    /// }
    ///
    /// fn parse_impl(file: File) -> Result<T, ParseError> {
    ///     # const IGNORE: &str = stringify! {
    ///     ...
    ///     # };
    ///     # unimplemented!()
    /// }
    ///
    /// pub fn parse(path: impl AsRef<Path>) -> anyhow::Result<T> {
    ///     let file = File::open(&path)?;
    ///     parse_impl(file).map_err(|error| {
    ///         let context = format!(
    ///             "only the first {} lines of {} are valid",
    ///             error.line, path.as_ref().display(),
    ///         );
    ///         anyhow::Error::new(error).context(context)
    ///     })
    /// }
    /// ```