Richard Byrne posted this article on his blog.
This is a great explanation of each type of web document. There are some great examples at the bottom of the chart (Google Spreadsheet).
Here is a direct link to the chart: https://docs.google.com/Doc?docid=ddnzwcn8_15g3jrbpdf
Sorry for the short post: It is my birthday. This Link is REALLY a good one, though!