title: React what's the right way to get a parent props from its children
body: <p>Be patient I'm new at React.</p>
  
  <p>In this snippet (it doesn't work) I want,</p>
  
  <p>in the CommentForm, to get the value of url props</p>
  
  <p>from the CommentBox.</p>
  
  <pre><code>var CommentBox = React.createClass({
    render: function() {
      return (
        &lt;div className="commentBox"&gt;
          &lt;h1&gt;Comments&lt;/h1&gt;
          &lt;CommentList /&gt;
          &lt;CommentForm /&gt;
        &lt;/div&gt;
      );
    }
  });
  
  var CommentList = React.createClass({
    render: function() {
      return (
        &lt;div className="commentList"&gt;
          Hello, world! I am a CommentList.
        &lt;/div&gt;
      );
    }
  });
  
  var CommentForm = React.createClass({
    render: function() {
      return (
        &lt;div className="commentForm"&gt;
          Hello,  my test url {this.props.url} !.
        &lt;/div&gt;
      );
    }
  });
  
  React.render(
    &lt;CommentBox url="api/comments" /&gt;,
      document.getElementById('content')
  );
  </code></pre>
  
  <p>What's the right way ?</p>
  
  <p>and why the props is not available directly from the parent to the children ?</p>