icu_locid/extensions/transform/key.rs
// This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
impl_tinystr_subtag!(
/// A key used in a list of [`Fields`](super::Fields).
///
/// The key has to be a two ASCII characters long, with the first
/// character being alphabetic, and the second being a number.
///
/// # Examples
///
/// ```
/// use icu::locid::extensions::transform::Key;
///
/// let key1: Key = "k0".parse().expect("Failed to parse a Key.");
///
/// assert_eq!(key1.as_str(), "k0");
/// ```
Key,
extensions::transform,
key,
extensions_transform_key,
2..=2,
s,
s.all_bytes()[0].is_ascii_alphabetic() && s.all_bytes()[1].is_ascii_digit(),
s.to_ascii_lowercase(),
s.all_bytes()[0].is_ascii_lowercase() && s.all_bytes()[1].is_ascii_digit(),
InvalidExtension,
["k0"],
["", "k", "0k", "k12"],
);