XML is a meta-markup language, a set of rules for creating semantic tags used to describe data. An XML element is made up of a start tag, an end tag, and data in between. The start and end tags describe the data within the tags, which is considered the value of the element. For example, the following XML element is a "director" element with the value "Ed Wood."
<director>Ed Wood</director>
The element name "director" allows you to mark up the value "Ed Wood" semantically, so you can differentiate that particular bit of data from another, similar bit of data. For example, there might be another element with the value "Ed Wood."
<actor>Ed Wood</actor>
Because each element has a different tag name, you can easily tell that one element refers to Ed Wood, the director of Jail Bait, while the other refers to Ed Wood, the lead actor in Glen or Glenda. If there were no way to mark up the data semantically, having two elements with the same value might cause some confusion.
In addition, XML tags are case-sensitive, so the following are each a different element.
<City> <CITY> <city>
An element can optionally contain one or more attributes. An attribute is a name-value pair separated by an equal sign (=).
<CITY ZIP="01085">Westfield</CITY>
In the example above, ZIP="01085" is an attribute of the "CITY" element. Attributes are used to attach additional, secondary information to an element, usually meta-information. Attributes can also accept default values, while elements cannot. Each attribute of an element can be specified only once, but in any order.
Because XML is a highly structured language, it is important that all XML be well-formed. That is, the XML must have both a start tag and an end tag, and must be authored using the proper syntax. In the box below, create an XML element with a start tag, an end tag, and a value on a single line. Click the Well-formed? button to see if your XML is correct.