If you've already read my XML tutorial, many will be familiar to you. The head and body tags are now mandatory. Every tag must be closed. If you only had one table on a page, you didn't need the end TD and end TR tags. All tags that require end tags get end tags.
Empty tags get a terminating slash.
An empty tag is a tag that doesn't require an end tag. All tags must be lower case. This does not apply to attributes, only tags. You may have noticed that I have quotes around all of the attributes. Attribute quotes are now mandatory.