2.2.1 [ISO10646] Section 14, Implementation Levels
ISO/IEC 10646 specifies three levels of implementation. Combining characters are described in clause 25 and listed in annex B. 14.1 Implementation level 1 When implementation level 1 is used, a CC-dataelement shall not contain coded representations of combining characters (see clause B.1) nor of characters from the HANGUL JAMO block (see clause 26.1). When implementation level 1 is used the uniquespelling rule shall apply (see clause 26.2). 14.2 Implementation level 2 When implementation level 2 is used, a CC-dataelement shall not contain coded representations of characters listed in clause B.2. When implementation level 2 is used the unique-spelling rule shall apply (see clause 26.2). 14.3 Implementation level 3 When implementation level 3 is used, a CC-dataelement may contain coded representations of any characters.
All Document Modes (All Versions)
Coded representations of characters not allowed in implementation
levels 1 or 2 (for example,
displayed. Therefore, Windows Internet Explorer is considered to be at
implementation level 3.