pub const BASE64: &[u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";Expand description
Standard base64 alphabet — RFC 4648 §4. A-Z, a-z, 0-9, +,
/. 64 characters.
Note: + and / require percent-encoding in URL contexts; prefer
URL_SAFE when generating identifiers that go into URLs.