lib
The nested lib element specifies a FileSet. All files included in this fileset will end up in the WEB-INF/lib directory of the war file.
classes
The nested classes element specifies a FileSet. All files included in this fileset will end up in the WEB-INF/classes directory of the war file.
webinf
The nested webinf element specifies a FileSet. All files included in this fileset will end up in the WEB-INF directory of the war file. If this fileset includes a file named web.xml, the file is ignored and you will get a warning.
metainf
The nested metainf element specifies a FileSet. All files included in this fileset will end up in the META-INF directory of the war file. If this fileset includes a file named MANIFEST.MF, the file is ignored and you will get a warning.