Speaking as someone who writes and puts stuff online, there are probably approximately 1.2 zillion subtle errors.
The best thing you can do is point them out so the author can fix it for posterity.
In a classic publishing environment, sure, edit the shit out of it before launch. But this isn't that environment. The fastest way to get quality, free content out there is to publish something and then have everyone tell you what's wrong, fix it, and move on.
Working together this way, we produce libraries of material for anyone to use.
What other more subtle errors are also there?