Also what it means by the line below from Mikalai Zaikin??
"However, the contents of the WEB-INF directory are visible to servlet code using the getResource and getResourceAsStream method calls on the ServletContext, and may be exposed using the RequestDispatcher calls."
"Document root" might also be referring to the root element of a JSP document (or maybe even another xml file). This is basically the outermost element/tag of the file. If you had given us more context around the statement, it would have been easier to provide a clearer answer.