The data extracted during the engine's handling of a request is stored as an XML stream. When you create an extractor (see how to create an extractor) or when you author XSLT style sheets to transform engine generated XML, you must know the generic form of the XML document.
A XML document always has a unique root; the engine creates this root for you, its name is always BODY with no namespace associated:
After all extractors have been called, the engine always extracts the parameters in the XML stream under a PARAMETERS tag with no namespace; for each parameter, a tag is created with is name in upper case, a method attribute containing the method of the parameter (POST, GET, COOKIES), and its content is the parameter value:
<BODY> <PARAMETERS> <MY_FIRST_PARAMETER method="POST">my first parameter value</MY_FIRST_PARAMETER> <MY_SECOND_PARAMETER method="GET">my first parameter value</MY_SECOND_PARAMETER> ... </PARAMETERS> </BODY>
The built-in extractors always create tag names in uppercase with no namespace, but you are free to mix cases and use namespaces if you wish; just know that tag names in XPath expressions are case sensitive.