The Hong Kong Supplementary Character Set (香港增補字符集; commonly abbreviated to HKSCS) is a set of Chinese characters – 4,702 in total in the initial release—used in Cantonese, as well as when writing the names of some places in Hong Kong (whether in written Cantonese or standard written Chinese sentences).
[1] It evolved from the preceding Government Chinese Character Set (政府通用字庫) or GCCS.
106 GCCS characters were removed in HKSCS-1999 as a result of unification, and their Big5 code points are reserved for compatibility.
Since around 2005, many Hong Kong and Macau websites have switched encoding from Big5-HKSCS to Unicode, including HKGolden.
These were all minor variants of existing Big5 characters containing the 昷/𥁕, 兑/兌 and 吿/告 components, for which Hong Kong font conventions were closer to those of mainland China than to those of Taiwan, but for which the preferred versions had been encoded separately from the Big5 versions in the Unified Repertoire and Ordering due to the source separation rule.
[13] By November, a total of 78 requested additions to HKSCS had been received by the Hong Kong government, all of which already existed in Unicode.
The first batch of 121 MSCS characters were submitted for addition to or horizontal extension in Unicode (as appropriate) in 2009.
[11][17] Although the potential scope of these source prefixes collectively comprises a superset of HKSCS-2016, "MSCS" in a strict sense does not cover the Big5 or HKSCS characters (since it is intended to be combined with HKSCS) except those which are used as base characters for ideographic variation sequences.
For earlier versions of the OS, HKSCS support requires the use of Microsoft's patch, or the Hong Kong government's Digital 21's utilities.
Modern desktop distributions (e.g. Ubuntu) include Arphic Technology's HKSCS-compliant UKai and UMing fonts out of the box when Traditional Chinese Language support is selected during installation.
However, the fix for bug 343129 does not support characters mapped to code points above Basic Multilingual Plane.
[30] QT 3.x-based applications (e.g.: KDE) only support characters mapped to code points FFFF or lower.
[31] GNOME supports HKSCS characters in Unicode ranges, except those mapped to the Basic Multilingual Plane compatibility block.
Patches to support characters mapped to above Basic Multilingual Plane was introduced during Pango 1.1.