A canonical decomposition mapping from a character to a different single character.

• The default value for the Decomposition_Mapping property for a code point (including any private-use character, any noncharacter, and any unassigned code point) is the code point itself. This default value does not count as a singleton decomposition, because it does not map a character to a different character. Private agreements cannot override the decomposition mapping for private-use characters
• Example: U+2126 ohm sign has a singleton decomposition to U+03A9 greek capital letter omega.
• A character with a singleton decomposition is often referred to simply as a singleton for short.