Table 1.1 XML Tags TYPE FORM EXAMPLE CONSTRAINTS Start tag Must start with <, <Root> Must have a end with >, not start matching end tag or end with </ or />. of the same name. End tag Must start with </, </Root> Must have a end with >, and not matching start tag end with />. of the same name. Empty element tag Must start with <, <Child end with />, and not Element1 /> start with </. Processing Instructions You may have noticed that all of our sample documents begin with the same line. This is a processing instruction. Processing instructions give input to the application that is handling the document. The <?xml  version=”1.0”  ?> processing instruction is required. It can also have an additional attribute to describe the character encoding of the document. Here is an example that reinforces the default encoding: <?xml version=”1.0” encoding=”UTF-8” ?> Your documents can have more than one processing instruction. For XSQL pages, your  documents  will  usually  have  a  processing  instruction  that  references  an  XSLT stylesheet. This will be covered in depth later this chapter. <?xml-stylesheet type=”text/xsl” href=”emp.xsl”?> Attributes Attributes are name-value pairs that are associated with an XML element. Most HTML elements also have attributes. The bgcolor attribute of the body element is one of many examples. You can have as many attributes in your element as you wish. However, each attribute name can appear only once for a particular element. Values always have to  be  quoted  with  either  single  or  double  quotes.  Attribute  names  and  values  are restricted in that they can only contain some characters. These restrictions are the same as the restrictions on the names of XML elements and are covered in the next section. Introducing Oracle XSQL 17 271209 Ch01.F  12/9/02  2:00 PM  Page 17