D800DBFF

D800DBFF is a hexadecimal string commonly used in discussions of Unicode and UTF-16 encoding. It denotes the range of Unicode code points that serve as high surrogates in UTF-16, specifically the values U+D800 through U+DBFF.

In UTF-16, characters outside the Basic Multilingual Plane (U+10000 to U+10FFFF) are encoded as pairs of 16-bit code units: a high surrogate (in the range D800–DBFF) followed by a low surrogate (in the range DC00–DFFF). The high-surrogate range contains 1024 code points, and each high surrogate pairs with one low surrogate to represent a single supplementary character.

The mapping from a surrogate pair to a Unicode code point is defined by a formula: code point = 0x10000 + ((high − 0xD800) << 10) + (low − 0xDC00). This mechanism enables the encoding of characters beyond the Basic Multilingual Plane. The pair itself does not correspond to a standalone character; it is a component of the UTF-16 encoding of extended characters.

In practical terms, the high-surrogate range is referenced in Unicode specifications and is frequently encountered in software dealing with UTF-16 data, such as text processing libraries, regex patterns targeting surrogate ranges, and string literals that encode code units. While an eight-hex-digit sequence like D800DBFF could appear as part of a larger hexadecimal value in other contexts, its canonical interpretation in Unicode terminology is the range of high surrogates U+D800 to U+DBFF.