Next, you need to define elements for your purchases document.
Elements specify the keywords for markup tags that can be used in the body of the document.
XML has no predefined element names. In XML, you could represent the purchase-related information with a purchase element and the customer contact information with a customer element. Here, the items between parentheses describe the contents of the main element. XML provides many additional operators to describe how often and in what context elements occur. Figure 2 lists these operators and shows their uses.