R proper way to parse xml - r

Question

I have an xml response containing Body and Header nodes, how can I access the value of the $Envelope$Body$checkVatResponse$valid node?
For some reason I already can't find the Body using xml_find_all
library(httr)
library(dplyr)
library(rvest)
library(xml2)
body = r'[<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" >
<soapenv:Header/>
<soapenv:Body>
<urn:checkVat xmlns:urn="urn:ec.europa.eu:taxud:vies:services:checkVat:types">
<urn:countryCode>NL</urn:countryCode>
<urn:vatNumber>800938495B01</urn:vatNumber>
</urn:checkVat>
</soapenv:Body>
</soapenv:Envelope>]'
r <- POST("http://ec.europa.eu/taxation_customs/vies/services/checkVatTestService", body = body)
stop_for_status(r)
content(r) %>% xml_find_all('//Body')
content(r) %>% xml2::as_list()
res <- content(r)
xml_children(res) %>% xml_name()
# [1] "Header" "Body"
xml_find_all(res,'.//Body')
# {xml_nodeset (0)}

Answer 1

When working with XML data, you need to be mindful of the namespaces used in the file. You need to previx namespaced nodes with the correct namespace. To extract the valid value you can use
content(r) %>% xml_find_all('//env:Body/ns2:checkVatResponse/ns2:valid')
To see all the namespaces used by the file you can run
content(r) %>% xml_ns()
# env <-> http://schemas.xmlsoap.org/soap/envelope/
# ns2 <-> urn:ec.europa.eu:taxud:vies:services:checkVat:types