text: (unassigned) Private use, alias, special codes
  Special codes
  : 50 Codes reserved for private use (for example,  is used to mark Burmese text encoded for the Zawgyi font)
  : Emoji
  : Code for inherited script
  : Mathematical notation
  : Symbols
  : Code for unwritten documents
  : Code for undetermined script
  : Code for uncoded script
  Exceptionally reserved codes
  Two four-letter codes are reserved at the request of the Common Locale Data Repository (CLDR) project:
  : Reserved for the language-neutral base of the CLDR locale tree
  : Reserved for the Boolean value "true"
  List of codes
  This list of codes is from the ISO 15924 standard.
  Relations to other standards
  The following standards are referred to as indispensable by ISO 15924.
  ISO 639-2:1998 Codes for the representation of names of languages — Part 2: Alpha-3 code
  ISO/IEC 9541-1:1991 Information technology — Font information interchange — Part 1: Architecture
  ISO/IEC 10646-1:2020 Information technology — Universal Multiple-Octet Coded Character Set (UCS)
  For definition of font and glyph the standard refers to
  ISO/IEC 9541-1:1991
  Around 160 scripts are defined in Unicode. Through a linkpin called "Property Value Alias", Unicode has made a 1:1 connection between a script defined, and its ISO 15924 standard. See Script (Unicode).