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    /// True values are `y`, `yes`, `t`, `true`, `on`, and `1`.
    pub(crate) const TRUE_LITERALS: [&str; 6] = ["y", "yes", "t", "true", "on", "1"];

    /// False values are `n`, `no`, `f`, `false`, `off`, and `0`.
    pub(crate) const FALSE_LITERALS: [&str; 6] = ["n", "no", "f", "false", "off", "0"];

    /// Converts a string literal representation of truth to true or false.
    ///
    /// `false` values are `n`, `no`, `f`, `false`, `off`, and `0` (case insensitive).
    ///
    /// Any other value will be considered as `true`.
    pub(crate) fn str_to_bool(val: impl AsRef<str>) -> Option<bool> {
        let pat: &str = &val.as_ref().to_lowercase();
        if TRUE_LITERALS.contains(&pat) {
            Some(true)
        } else if FALSE_LITERALS.contains(&pat) {
            Some(false)
        } else {
            None
        }
    }