nonBMP

Non-BMP refers to Unicode code points that lie outside the Basic Multilingual Plane (BMP). Specifically, non-BMP code points are those from U+10000 to U+10FFFF, spanning planes 1 through 16. These supplementary planes contain a large set of characters, including emoji, additional CJK ideographs, extended mathematical symbols, musical notation, historic scripts, and other specialized symbols.

Encoding and representation vary by encoding form. In UTF-16, non-BMP code points are encoded using surrogate pairs, with a lead surrogate in the range D800–DBFF and a trailing surrogate in DC00–DFFF. In UTF-8, non-BMP code points require four bytes. In UTF-32, each code point maps directly to a single 32-bit value.

Practical implications include rendering and font support, since many fonts do not include glyphs for all non-BMP characters. Emoji handling is a notable area, where variation selectors may determine text versus emoji presentation, and sequences with joiners can produce additional symbols. Text-processing considerations are also important: systems that index by code units (such as UTF-16) may treat a single non-BMP character as two units, affecting length, slicing, and iteration. Sorting, normalization, and search can be more complex for non-BMP data due to their diverse properties and combining marks.

The concept of non-BMP emerged with Unicode’s supplementary planes and has grown in importance as emoji and other extended scripts become widespread in digital communication and scholarly work.