Why does the CLAWS5 tagset separate "of" from all other prepositions?

Question

The well-known CLAWS5 tagset, for tagging English language lexemes etc, has one tag PRF, specifically for tagging the preposition "of", while other prepositions get the tag PRP, which is for all prepositions except "of".

Apparently, this kind of thing has some use, since two revisions later, CLAWS7 has separate tags also for "with/without" and "for".

What is the motivation behind these distinctions?

Answer 1

The function word "of" is sometimes difficult to classify, think of cases like to be aware of something, to be fond of something/someone, or because of. Putting it in a category of its own reduces the errors of misclassification.