title: Select-Xml shows only the child nodes that are in the first node
body: <p>The following will display a child element if and only if it's in the first parent element.</p>
  
  <pre><code>$xml = @"
  &lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;root&gt;
      &lt;par&gt;&lt;commonchild&gt;Hi there.&lt;/commonchild&gt;&lt;otherchild&gt;This is displayed.&lt;/otherchild&gt;&lt;/par&gt;
      &lt;par&gt;&lt;commonchild&gt;Hi again.&lt;/commonchild&gt;&lt;otherchild&gt;So is this.&lt;/otherchild&gt;&lt;/par&gt;
      &lt;par&gt;&lt;commonchild&gt;Well hello.&lt;/commonchild&gt;&lt;missingchild&gt;This is missing.&lt;/missingchild&gt;&lt;/par&gt;
      &lt;par&gt;&lt;commonchild&gt;Cheers.&lt;/commonchild&gt;&lt;missingchild&gt;So is this.&lt;/missingchild&gt;&lt;/par&gt;
  &lt;/root&gt;
  "@
  
  cls
  Select-Xml -Content $xml -XPath "//par" | select -ExpandProperty node
  </code></pre>
  
  <p>Output</p>
  
  <pre><code>commonchild otherchild        
  ----------- ----------        
  Hi there.   This is displayed.
  Hi again.   So is this.       
  Well hello.                   
  Cheers.        
  </code></pre>
  
  <p>How can we instead display all the child elements of all parents? For instance, the following works but sometimes we don't know all the child element names. </p>
  
  <pre><code>cls
  Select-Xml -Content $xml -XPath "//par" | 
      select -ExpandProperty node | 
      select commonchild, otherchild, missingchild
  </code></pre>
  
  <p>Output </p>
  
  <pre><code>commonchild otherchild         missingchild    
  ----------- ----------         ------------    
  Hi there.   This is displayed.                 
  Hi again.   So is this.                        
  Well hello.                    This is missing.
  Cheers.                        So is this.   
  </code></pre>