The POS features abstract away from the words and avoid the problem of data sparseness by allowing the classifier to focus on the categories of the words, rather than the lexical items themselves.
while there are certainly rule-based decision points for comma insertion (Doran, 1998), particularly in the case of commas that set off significant chunks or phrases within sentences, there are also some commas that appear to be more prescriptive, as they have less of an effect on sentence processing (such as in example (2) in the introduction), and opposing usage rules for the same contexts are attested in different style manuals.