The spec explains about this :
I think it refers to "JSP.1.1.5 Validating
JSP pages" :
All JSP pages, regardless of whether they are written in the traditional JSP syntax or the XML syntax of JSP documents have an equivalent XML document, the XML view of a JSP page, that is presented to tag library validators in the translation phase for validation.
The structure of the custom actions in a JSP page is always exposed in the XML view. This means that a tag library validator can check that, for instance, some custom actions are only used within others. And "JSP.6.1 Overview of JSP Documents and of XML Views" :
The XML view of a JSP page is an XML document that is derived from the JSP page following a mapping defined later in this chapter.. The XML view of a JSP page is intended to be used for validating the JSP page against some description of the set of valid pages. Validation of the JSP page is supported in the JSP 2.0 specification through a TagLibraryValidator class associated with a tag library. The validator class acts on a PageData object that represents the XML view of the JSP page (see, for example, Section JSP.7.4.1.2) "Figure JSP.6-1 Relationship between JSP Pages and XML views of JSP pages." shows how JSP pages are converted as an XML view before translation occurs.
Chapter 10 about XML Views. I have never read that. I didn't know about it either.