lowsurrogate

Lowsurrogate is a 16-bit code unit in UTF-16 Unicode encoding, occupying the range U+DC00 to U+DFFF. It serves as the trailing part of a surrogate pair, used to encode code points outside the Basic Multilingual Plane (U+10000 to U+10FFFF).

A valid surrogate pair consists of a high surrogate (U+D800–U+DBFF) followed by a low surrogate (U+DC00–U+DFFF). The corresponding code point is computed as: code point = ((high - 0xD800) << 10) + (low - 0xDC00) + 0x10000. For example, U+1F600 (GRINNING FACE) is encoded in UTF-16 as the pair 0xD83D 0xDE00, where 0xD83D is the high surrogate and 0xDE00 is the low surrogate.

Lowsurrogates are not standalone characters. Unpaired surrogates or misordered pairs constitute invalid sequences in well-formed UTF-16 and can cause decoding errors or security issues if not handled properly. Many languages and libraries provide means to process text by Unicode code points rather than by code units to avoid such problems.

See also high surrogate, UTF-16, Unicode supplementary planes.