Tens of thousands of graphic characters are used in publishing text, a large proportion of which have been defined in ISO/IEC 10646. Even where standard coded representations exist, however, there may be situations in which they cannot be keyboarded conveniently or accurately, or in which it is not possible to display the desired visual depiction of the characters.
To help overcome these barriers to the successful interchange of SGML and related documents, this part of ISO/IEC TR 9573 defines character entity sets for some widely used special graphic characters regularly used in the production of scientific and mathematical documents.
Note 1: Entity repertoires are necessarily larger and more repetitious than character sets, as they deal in general with higher-level constructs. For example, unique entities have been defined for each accented Latin alphabetic character, while a character set might represent such characters as combinations of letters and diacritical mark characters.
In many instances upper- and lower-case is used to differentiate the names of entities. It is assumed that any SGML concrete syntax used in conjunction with these entity names will be case sensitive.
Note 2: The reference concrete syntax defined in ISO/IEC 8879 (SGML) is case sensitive.