I try really hard to be fair and consistent when editing reviews. The one thing I always get caught up on is comma usage. What I would like to know: is comma usage entirely subjective? Meaning, is marking any comma usage as an error is unfair? Are there only certain comma rules that are objective? If I am not 100% sure of a grammar rule, I try to look it up and have proof before marking anything as incorrect. Yet, I still find myself with discrepancies and recheck requests for my "subjective and opinion-based" editing. I always try to err on the side of no error when questioned, but I'm discouraged!
I know this is probably not possible, but I wish there was a hard and fast guide for comma/punctuation errors. In the mean time, I will continue to research and cry! (JK

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