High Private Use Surrogates

Surrogates (high and Low). The UCS includes 2,048 code points in the Basic Multilingual Plane (BMP) for surrogate code point pairs. Together these surrogates allow any code point in the sixteen other planes to be addressed by using two surrogate code points. This provides a simple built-in method for encoding the 20.1 bit UCS within a 16 bit encoding such as UTF-16. In this way UTF-16 can represent any character within the BMP with a single 16-bit byte.

Characters outside the BMP are then encoded using two 16-bit bytes (4 octets total) using the surrogate pairs. Private Use. The consortium provides several private use blocks and planes that can be assigned characters within various communities, as well as operating system and font vendors.