| Well formedness rules | Example |
|---|---|
| 1. all elements must have a closing tag |
<p>text</p> <hr /> |
| 2. all elements must be properly nested | <b>bold text <i>bold italic text</i></b> |
| 3. single root (document) element allowed |
<html> <head> ... </head> <body> ... </body> </html> |
| 4. tag and attribute names are case sensitive |
<size>320 ml</size> <Size>extra large</Size> <SIZE>relative</SIZE> |
| 5.1 attributes can only go in the start tag and must be of the form name="value" and value is quoted | <car colour='silver trim'> |
| 5.2 attribute names must be unique in the tag | <garment usSize="6" ukSize="10"> |
| XML declaration | |
| first thing in the document - indicates version of xml and optional encoding | <?xml version="1.0" encoding="UTF-8"?> |
| Processing Instructions | |
| asks the processing application to do something | <?xml-stylesheet href="mystyle.css" type="text/css" ?> |
| Comments | |
| Same as HTML | <!-- comment --> |
| Character references and Entities | |
| Character refs allow any character to be inserted | Φ |
| Entities allow special symbols and predefined text to be entered | < ©w; |
| CDATA sections | |
| For including text not to be treated as XML | <![CDATA[ <wrong attr=val />]]> |