सरोगेट पेयर

दो UTF-16 कोड यूनिट (एक हाई सरोगेट U+D800-U+DBFF और उसके बाद एक लो सरोगेट U+DC00-U+DFFF) जो मिलकर U+FFFF से ऊपर के किसी वर्ण का प्रतिनिधित्व करते हैं।

Characters with code points above U+FFFF cannot fit in a single 16-bit value. UTF-16 solves this by encoding them as two 16-bit values called a surrogate pair. Since most emoji are above U+FFFF, surrogate pairs are extremely common with emoji.

For example, 😀 (U+1F600) becomes the surrogate pair 0xD83D 0xDE00 in UTF-16. The formula: high surrogate = 0xD800 + ((cp - 0x10000) >> 10), low surrogate = 0xDC00 + ((cp - 0x10000) & 0x3FF).

This is why JavaScript's `'😀'.charCodeAt(0)` returns 55357 (0xD83D) — it's returning the high surrogate, not the actual code point.