Private Use Areas


In Unicode, a Private Use Area is a range of code points that, by definition, will not be assigned characters by the Unicode Consortium. Three private use areas are defined: one in the Basic Multilingual Plane, and one each in, and nearly covering, planes 15 and 16. The code points in these areas cannot be considered as standardized characters in Unicode itself. They are intentionally left undefined so that third parties may define their own characters without conflicting with Unicode Consortium assignments. Under the Unicode Stability Policy, the Private Use Areas will remain allocated for that purpose in all future Unicode versions.
Assignments to Private Use Area characters need not be "private" in the sense of strictly internal to an organisation; a number of assignment schemes have been published by several organisations. Such publication may include a font that supports the definition, and software making use of the private-use characters. By definition, multiple private parties may assign different characters to the same code point, with the consequence that a user may see one private character from an installed font where a different one was intended.

Definition

Under the Unicode definition, code points in the Private Use Areas are assigned characters—they are not noncharacters, reserved, or unassigned. Their category is "Other, private use ", and no character names are specified. No representative glyphs are provided, and character semantics are left to private agreement.
Private-use characters are assigned Unicode code points whose interpretation is not specified by this standard and whose use may be determined by private agreement among cooperating users. These characters are designated for private use and do not have defined, interpretable semantics except by private agreement.
No charts are provided for private-use characters, as any such characters are, by their very nature, defined only outside the context of this standard.

Assignment

In the Basic Multilingual Plane, the block titled Private Use Area has 6400 code points. Planes 15 and 16 are almost entirely assigned to two further Private Use Areas, Supplementary Private Use Area-A and Supplementary Private Use Area-B respectively.
In order to encode characters from planes 15 and 16 in UTF-16, a further block of the BMP is assigned to High Private Use Surrogates.

Usage

Standardization initiative uses

Many people and institutions have created character collections for the PUA. Some of these private use agreements are published, so other PUA implementers can aim for unused or less used code points to prevent overlaps. Several characters and scripts previously encoded in private use agreements have actually been fully encoded in Unicode, necessitating mappings from the PUA to other Unicode code points.
One of the more well-known and broadly implemented PUA agreements is maintained by the ConScript Unicode Registry. The CSUR, which is not officially endorsed or associated with the Unicode Consortium, provides a mapping for constructed scripts, such as Klingon pIqaD and Ferengi script, Tengwar and Cirth, Alexander Melville Bell's Visible Speech, and Dr. Seuss' alphabet from On Beyond Zebra. The CSUR previously encoded the undeciphered Phaistos characters, as well as the Shavian and Deseret alphabets, which have all been accepted for official encoding in Unicode.
Another common PUA agreement is maintained by the Medieval Unicode Font Initiative. This project is attempting to support all of the scribal abbreviations, ligatures, precomposed characters, symbols, and alternate letterforms found in medieval texts written in the Latin alphabet. The express purpose of MUFI is to experimentally determine which characters are necessary to represent these texts, and to have those characters officially encoded in Unicode. As of Unicode version 5.1, 152 MUFI characters have been incorporated into the official Unicode encoding.
Some agreed-upon PUA character collections exist in part or whole because Unicode Consortium is in no hurry to encode them. Some, such as unrepresented languages, are likely to end up encoded in the future. Some unusual cases such as fictional languages are outside the usual scope of Unicode but not explicitly ruled out by the principles of Unicode, and may show up eventually. In other cases, the proposed encoding violates one or more Unicode principles and hence is unlikely to ever be officially recognized by Unicode—mostly where users want to directly encode alternate forms, ligatures, or base-character-plus-diacritic combinations.
Publishing organisationTopicPUA area usedFont
CSURArtificial scriptsPUA and Plane 15Code2000
MUFIMedieval scriptsPUA several
SILPhonetics and languagesPUA
TITUSAncient and medieval scriptsPUA TITUS Cyberbit Basic

Informally, the range U+F000 through U+F8FF is known as Corporate Use Area.
There are three PUA blocks in Unicode.

Private-use characters in other character sets

The concept of reserving specific code points for Private Use is based on similar earlier usage in other character sets. In particular, many otherwise obsolete characters in East Asian scripts continue to be used in specific names or other situations, and so some character sets for those scripts made allowance for private-use characters. The Unicode standard references these uses under the name "End User Character Definition".
Additionally, the C1 control block contains two codes intended for private use "control functions" by ECMA-48: 0x91 and 0x92 . Unicode includes these at and but defines them as control characters, not private-use characters.
Encodings which do not have private use areas but have more or less unused areas, such as ISO/IEC 8859 and Shift JIS, have seen uncontrolled variants of these encodings evolve. For Unicode, software companies can use the Private Use Areas for their desired additions.