/// This encoding matches GB18030-2022 except the two-byte sequence 0xA3 0xA0
/// maps to U+3000 for compatibility with existing Web content and the four-byte
/// sequences for the non-PUA characters that got two-byte sequences still decode
/// to the same non-PUA characters as in GB18030-2005. As a result, this encoding
/// can represent all of Unicode except for 19 private-use characters.
///
/// [Index visualization for the two-byte sequences](https://encoding.spec.whatwg.org/gb18030.html),
/// [Visualization of BMP coverage of the two-byte index](https://encoding.spec.whatwg.org/gb18030-bmp.html)
///
/// This encoding matches the Windows code page 54936.