title: What does it mean by "indirectly declaring a namespace within another namespace"?
body: <p>[basic.link] paragraph 4 in the C++14 Standard:</p>
  
  <blockquote>
    <p>An unnamed namespace or a namespace declared directly or indirectly
    within an unnamed namespace has internal linkage. All other namespaces
    have external linkage. A name having namespace scope that has not been
    given internal linkage above has the same linkage as the enclosing
    namespace if it is the name of ...</p>
  </blockquote>
  
  <p>What does it mean by "indirectly declaring a namespace within another namespace" above?</p>