Ever wonder at the correct usage of punctuation or syntax and grammar is? A good guide to usage, although lengthy, is the Chicago Manual of Style. Not all disciplines use this style, but it does provide some useful information for those willing to go through it.
There is actually an online copy available where you can do a Quick Search or you can look through the Table of Contents/Index. If ever in doubt, check a style guide!
Here is the link: http://www.chicagomanualofstyle.org/home.html
Update: Now that I've written about it, I seem to be encountering a few pages where you have to subscribe to see the info. But even if you can't see that rule, you know how to look it up on Google, so not all is lost!