/// Lowercase a PHP identifier (method name, function name, class name, keyword).
///
/// PHP technically allows bytes `0x80–0xFF` in identifiers, but real-world PHP is
/// overwhelmingly ASCII. `to_ascii_lowercase` is correct for all ASCII identifiers and
/// faster than the Unicode-aware `to_lowercase`; bytes above 0x7F pass through unchanged.
///
/// **Do not use** for docblock content, string literals, or arbitrary source text —
/// those may contain non-ASCII characters that require full Unicode case folding.
pub
/// Every native PHP superglobal name (without the `$` prefix), for purity
/// checks that treat reading/writing one as touching external mutable
/// state — deliberately broader than `taint::SUPERGLOBALS` (which excludes
/// `$_SESSION`/`GLOBALS`/`argv`/`argc` since those aren't attacker-controlled
/// taint sources; purity cares about "is this external state", not "is this
/// user input", so the two lists have different membership on purpose).
pub