Each pattern defined in the address patterns file must have an associated pattern class. The pattern class indicates a portion of the input pattern or the type of address data that is represented by the pattern. You can specify any of the following pattern classes.
W - the address pattern represents a unit within a structure, such as an apartment or suite number
T - the address pattern represents a street type or direction
These classes are also specified as usage flags in the patterns file and the master clues file.