title: Why does Markov blanket contain the children's parents?
body: <p>I am quite confused about why Markov blanket contains children's parents. <a href="https://en.wikipedia.org/wiki/Markov_blanket" rel="noreferrer">Wikipedia</a> says</p>
  
  <blockquote>
    <p>its children's parents also have to be included, because they can be used to explain away the node in question.</p>
  </blockquote>
  
  <p>But what's <code>the node in question</code>? I also found another info from <a href="http://library.bayesia.com/display/FAQ/Markov+Blankets" rel="noreferrer">BayesiaLab</a>. It says</p>
  
  <blockquote>
    <p>The Spouses (or co-parents, dark green) are used for cutting the information coming from the ascendants of the Children (blue nodes). The Target node is marginally independent of the Spouses, but becomes conditionally dependent, i.e. when some evidence is available on the Children.</p>
  </blockquote>
  
  <p>Why do the Target node and the Spouse become conditionally dependent when some evidence is available on the Children? What does it mean that <em>some evidence is available on the Children</em>?</p>
  
  <p>I hope someone could help clarify it, esp. with a concrete example. Thanks:)</p>