An xhtml document must:
- contain a root element, that is <html>. The elements with the tags <head>, <body>, ... are called the children of the root element.
- be in lower case
- be closed even for the empty elements that can also start with />, like:
- a break <br />
- an horizontal rule <hr />
- nested correctly
- have attribute values quotted, like: <font color = "red"></font>
- have no minimization, like: <option selected="selected"/>
- have no name attribute, but an id attribute, like: <img src="goldMouth.gif" id="gold" />
- have a dtd element.
Always an extra space before the "/" symbol for an empty HTML element, that is the the element that has no closing tag.
