Each element is enclosed in <> brackets. The element must be end with '/' character before its name. XML requires one element like that contains all others. This single element("LAND"), is called the root element. The FOREST element contains several TREE elements, and the MEADOW likewise contains several elements of GRASS.

Elements that are included in another element are called nested element. The TREE elements nested in the above example are nested in the FOREST element.The FOREST element is the parent element to the TREE element and the TREE element is also called the sub-element to the FOREST element. These relationships hold true as you move up and down the element hierarchy. The FOREST and MEADOW elements are sub-elements to the LAND root element.

<TREE>Oak tree</TREE>

Elements without content may be expressed as:

<NOTHING></NOTHING>

In short it may be expressed as:

<NOTHING/>

Elements with no content may be used to display graphics and other material in the document.
 

• What is HTML



• What is XML

• Elements must have a closing tag



• Elements must be properly nested

Book is the root element. Title, prod id, and chapter are child elements. Book is the parent element of title, prod, and chapter. Title, prod, and chapter are siblings because they have the same parent.

Elements may contain:

• Nested elements



• Processing instructions



• Normal text.




• CDATA sections - it consistspecial characters which is not displayed normally by the browser such as less than or greater than sign. These signs are used to enclose tags and are special characters. An example CDATA section:
  
  

• Entity references - An entitity reference is not allowed by a & sign.




• Character references - Character References are not displayed normally in XML such as the < or > characters. These characters are represented as &#40 and &#42 respectively and will be presented on the browser as the less than or greater than character they represent.




• Comments - Comments are shown below and may be placed anywhere except an element tag (markup).


<!-- comment not display by browser -->

• it consist letters, numbers, and other characters
• Names must not start with a number or punctuation character
• Names must not start with the letters xml (or XML, or Xml, etc)
• Names cannot contain spaces

Take care when you "invent" element names and follow these simple rules:

Any name can be used, no words are reserved, but the idea is to make names descriptive. Names with an underscore separator are nice.

Examples: <first_name>, <last_name>.

Avoid "-" and "." in names. For example, if you name something "first-name," it could be a mess if your software tries to subtract name from first. Or if you name something "first.name," your software may think that "name" is a property of the object "first."

Element names can be as long as you like, but don't exaggerate. Names should be short and simple, like this: <book_title> not like this: <the_title_of_the_book>. 

XML documents often have a corresponding database, in which fields exist corresponding to elements in the XML document. A good practice is to use the naming rules of your database for the elements in the XML documents.

Non-English letters like éòá are perfectly legal in XML element names, but watch out for problems if your software vendor doesn't support them.

The ":" should not be used in element names because it is reserved to be used for something called namespaces (more later).