An XML document contains XML Elements.
What is an XML Element?
An XML element is everything from (including) the element's start tag to (including) the element's end tag.
An element can contain:
- other elements
- or a mix of all of the above...
In the example above, <bookstore> and <book> have element contents, because they contain other elements. <book> also has an attribute (category="CHILDREN"). <title>, <author>, <year>, and <price> have text content because they contain text.
XML Naming Rules
XML elements must follow these naming rules:
- Names can contain letters, numbers, and other characters
- Names cannot start with a number or punctuation character
- Names cannot start with the letters xml (or XML, or Xml, etc)
- Names cannot contain spaces
Any name can be used, no words are reserved.
Best Naming Practices
Make names descriptive. Names with an underscore separator are nice: <first_name>, <last_name>.
Names should be short and simple, like this: <book_title> not like this: <the_title_of_the_book>.
Avoid "-" characters. If you name something "first-name," some software may think you want to subtract name from first.
Avoid "." characters. If you name something "first.name," some software may think that "name" is a property of the object "first."
Avoid ":" characters. Colons are reserved to be used for something called namespaces (more later).
XML documents often have a corresponding database. 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, but watch out for problems if your software vendor doesn't support them.
XML Elements are Extensible
XML elements can be extended to carry more information.
Look at the following XML example:
Let's imagine that we created an application that extracted the <to>, <from>, and <body> elements from the XML document to produce this output:
Don't forget me this weekend!
Imagine that the author of the XML document added some extra information to it:
Should the application break or crash?
No. The application should still be able to find the <to>, <from>, and <body> elements in the XML document and produce the same output.
One of the beauties of XML, is that it can be extended without breaking applications.