Private Use Areas

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For Private Use characters used in Wikipedia pages, see MOS:PUA

In Unicode, the Private Use Areas (PUA) are three ranges of code points (U+E000U+F8FF in the BMP, and in planes 15 and 16) that, by definition, will not be assigned characters by the Unicode Consortium. The code points in these areas can not 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,[1] 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 (showing the glyphs), and software making use of the private-use characters (e.g. a graphics character for a "print document" function). 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[edit]

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 (Co)", 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.[2]

Assignment[edit]

In the Basic Multilingual Plane (plane 0), the block titled Private Use Area has 6400 code points. Planes 15 and 16 are almost[note 1] entirely assigned to two further Private Use Areas, Supplemental Private Use Area-A and Supplemental 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 (U+DB80..U+DBFF, 128 code points).

Usage[edit]

Standardization initiative uses[edit]

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 (CSUR). 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 (Star Trek), Tengwar and Cirth (J.R.R. Tolkien's cursive and runic scripts), 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 (MUFI). 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.

Publishing organisation Topic PUA area claimed Font
CSUR Artificial scripts PUA (BMP) and Plane 15 Code2000
MUFI Medieval scripts PUA (BMP) several
SIL Phonetics and languages PUA (BMP) Charis SIL
TITUS Ancient and medieval scripts PUA (BMP) U+Exyz TITUS Cyberbit Basic
  • Emoji is an encoding for picture characters or emoticons used in Japanese wireless messages and webpages. With Unicode 6.0 and later, many of these have been encoded in the block Miscellaneous Symbols And Pictographs and elsewhere in the SMP.
  • GB/T 20542-2006 ("Tibetan Coded Character Set Extension A") and GB/T 22238-2008 ("Tibetan Coded Character Set Extension B") are Chinese national standards that use the PUA to encode precomposed Tibetan ligatures.
  • The Institute of the Estonian Language uses the PUA to encode Latin and Cyrillic precomposed characters[3] that have no Unicode encoding.
  • The Free Tengwar Font Project uses a different mapping from the ConScript Unicode Registry that largely follows Michael Everson’s 2001-03-07 Tengwar discussion paper, but diverges in some details.
  • The MARC 21 standard uses the PUA to encode East Asian characters present in MARC-8[4] that have no Unicode encoding.
  • The SIL Corporate PUA uses the PUA to encode characters used in minority languages that have not yet been accepted into Unicode.
  • The STIX Fonts project uses the PUA to provide a comprehensive font set of mathematical symbols and alphabets, many of which are also available in the SMP now, e.g. in the Mathematical Alphanumeric Symbols block.
  • The Tamil Unicode New Encoding (TUNE)[5] is a proposed scheme for encoding Tamil that overcomes perceived deficiencies in the current Unicode encoding.

Vendor use[edit]

Informally, the range U+F000 through U+F8FF is known as Corporate Use Area.

  • The Adobe Glyph List used to use the PUA for some of its glyphs.
  • Apple lists a range of 1,280 characters in its developer documentation[6] of U+F400–U+F8FF within the PUA for Apple’s use. Of those, only 311 are used in the range U+F700–U+F8FF.[7]
  • WGL4 uses the PUA (U+F001 and U+F002) to encode two characters   which are duplicates of the ligatures fi (U+FB01) fl (U+FB02).[8]
  • In old versions of its RichEdit component, Microsoft mapped U+F020–U+F0FF within the PUA to symbol fonts. For any character in this range, RichEdit would show a character from a symbol font instead of the end-user-defined character (EUDC)[9][10]
  • AutoCAD uses U+F8FC–U+F8FE for ⌀ (diameter sign), ± (plus-minus sign) and ° (degree sign) respectively.

U+F8FF[edit]

The Unicode code point U+F8FF () is the last code point in the Private Use Area of the BMP. Its meaning and appearance vary depending on the font in use, but its usage in several fonts makes it the most notable code point in the Private Use Area.

U+F8FF usage examples[edit]

Private-use characters in other character sets[edit]

The Unicode Private Use Area concept was 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 (such as the user-defined planes of CNS 11643, or gaiji in certain Japanese encodings). The Unicode standard references these uses under the name "End User Character Definition" (EUCD).[2]

Additionally, the C1 control block contains two codes intended for private use "control functions" by ECMA-48: 0x91 private use one (PU1) and 0x92 private use two (PU2).[11][12] Unicode includes these at U+0091 <control-0091> and U+0092 <control-0092> but defines them as control characters (category Cc), not private-use characters (category Co).[13][14]

Notes[edit]

  1. ^ The last two characters of every plane are defined to be non-characters. The remaining 65,534 characters of each of planes 15 and 16 are assigned as private-use characters.

References[edit]