Vietnamese Standard Code for Information Interchange

The Vietnamese Standard Code for Information Interchange (VISCII) is a character set comprising the Vietnamese alphabet, punctuation, and other graphemes. Vietnamese requires slightly too many (134) letter/diacritic combinations to make a traditional extended ASCII character set for it. There are essentially 3 possible solutions to this.

VISCII went for the last option, replacing 6 of the least problematic (e.g., least likely to be recognised by an application and acted on specially) C0 control codes (STX, ENQ, ACK, DC4, EM, and RS) with 6 of the least used uppercase letter/diacritic combinations. While this may cause issues with some programs in handling VISCII text if they use those control codes, it creates fewer complications than either of the other two solutions. However, it leaves absolutely no space available for things other than accented letters such as symbols, superscripted numbers, curved quotes, proper dashes, etc.