ULS provides a number of functions for determining whether or not a Unicode character has a specific attribute.

A character attribute (or classification) describes categories to which a character belongs. These include both POSIX types like 'alpha' (alphabetic character) and 'digit' (numeric digit), and extended Unicode types like 'ideograph' (CJK ideograph) and 'nonspacing' (non-spacing character). There are also attributes for describing text layout, and others indicating the specific character sets to which a character belongs.

See the next section for a complete list of attributes.