Answer - CSS allows Unicode characters to be entered by number. For example, if a CLASS value in some Russian document contains Cyrillic letters EL PE (Unicode numbers 041B and 041F) and you want to write a style rule for that class, you can put that letter into the style sheet by writing: .\041B\041F {font-style: italic;} This works on all keyboards, so you don't need a Cyrillic keyboard to write CLASS names in Russian or another language that uses that script. The digits and letters after the backslash (\) are a hexadecimal number. Hexadecimal numbers are made from ordinary digits and the letters A to F (or a to f). Unicode numbers consist of four such digits. If the number starts with a 0, you may omit it. The above could also be written as: .\41B\41F {font-style: italic;} But be careful if the next letter after the three digits is also a digit or a letter a to f! This is OK: .\41B-\41F, since the dash (-) cannot be mistaken for a hexadecimal digit, but .\41B9\41F is only two letters, not three. Four digits is the maximum, however, so if you write: .\041B9\041F {font-style: italic;}