xml_ns_strip(x)

x <- read_xml(
 "<foo xmlns = 'http://foo.com'>
   <baz/>
   <bar xmlns = 'http://bar.com'>
     <baz/>
   </bar>
  </foo>")
# Need to specify the default namespaces to find the baz nodes
xml_find_all(x, "//d1:baz")
xml_find_all(x, "//d2:baz")

# After stripping the default namespaces you can find both baz nodes directly
xml_ns_strip(x)
xml_find_all(x, "//baz")