Great piece about the life of a copy editor. This paragraph is gold:
There is a fancy word for “going beyond your province”: “ultracrepidate.” So much of copy editing is about not going beyond your province. Anti-ultracrepidationism. Writers might think we’re applying rules and sticking it to their prose in order to make it fit some standard, but just as often we’re backing off, making exceptions, or at least trying to find a balance between doing too much and doing too little. A lot of the decisions you have to make as a copy editor are subjective. For instance, an issue that comes up all the time, whether to use “that” or “which,” depends on what the writer means. It’s interpretive, not mechanical—though the answer often boils down to an implicit understanding of commas.
The full piece, here: http://www.newyorker.com/magazine/2015/02/23/holy-writ