Hangul, Hangul Supplementary-A, and Hangul Supplementary-B were character blocks that existed in Unicode 1.0 and 1.1, and ISO/IEC 10646-1:1993. These blocks encoded precomposed modern Hangul syllables. These three Unicode 1.x blocks were deleted and superseded by the new Hangul Syllables block (U+AC00–U+D7AF) in Unicode 2.0 (July 1996) and ISO/IEC 10646-1:1993 Amd. 5 (1998), and are now occupied by CJK Unified Ideographs Extension A and Yijing Hexagram Symbols. Moving or removing existing characters has been prohibited by the Unicode Stability Policy for all versions following Unicode 2.0, so the Hangul Syllables block introduced in Unicode 2.0 is immutable.