The rules for U+ notation have changed a few times. Current rules are U+xxxx, U+xxxxx, or U+xxxxxx, as appropriate, to denote a character by its code point. In older version of Unicode, code points and code values were treated separately using U- and U+ notation, respectively. The number of digits required varied. Unicode 3.0 said U- notation always had to have 8 digits, and U+ always had to have 4. That's obsolete now though. —