I want to delete the "of" from the phrase "off of" in a non-formal article. I've been checking whether there was any definitive evidence that it was incorrect, or at least, that it was reasonable of me to want to edit it out. I've found references to it having been in use since at least Shakespeare's time, and to it being considered non-standard in modern English. Can anyone suggest a source I can point to if needed? Or is it something that should be ignored?