// 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::locale::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"],);