XML : XML R How to retrieve value when node has dash/hyphen in name

Just when I thought I understood XPath! I must be missing something really simple, but I can't select the value of the node "citedby-count" in the following:

  <?xml version="1.0" encoding="UTF-8"?>  <search-results xmlns="http://www.w3.org/2005/Atom" xmlns:cto="http://www.elsevier.com/xml/cto/dtd" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:prism="http://prismstandard.org/namespaces/basic/2.0/" xmlns:opensearch="http://a9.com/-/spec/opensearch/1.1/" xmlns:dc="http://purl.org/dc/elements/1.1/">      <entry>      <prism:url>http://api.elsevier.com/content/abstract/scopus_id/111111</prism:url>      <dc:title>Paper Title</dc:title>      <citedby-count>1</citedby-count>    </entry>    

I've tried

  doc["//citedby-count"]    

and

  doc["//{'citedby-count'}"]    

but both return

  list()  attr(,"class")  [1] "XMLNodeSet"    

Have I just been looking at this too long? Please help!