title: ReactJS - Unknown prop `activeClassName` on <a> tag. Remove this prop from the element
body: <p>I am using react 15.4.2 and react-router4.0.0 and This project was bootstrapped with <a href="https://github.com/facebookincubator/create-react-app" rel="noreferrer">Create React App</a>.</p>
  
  <p>Here is my Code.</p>
  
  <pre><code>import React from 'react';
  import ReactDOM from 'react-dom';
  import './index.css';
  import {BrowserRouter as Router,Route,Link} from 'react-router-dom'
  
  
   const AboutPage = () =&gt; {
   return(
      &lt;section&gt;
          &lt;h2&gt;This is About page&lt;/h2&gt;
          &lt;Link activeClassName="active" to="/about/nestedone"&gt;Nestedone&lt;/Link&gt;
          {' '}
          &lt;Link activeClassName="active" to="/about/nestedtwo"&gt;Nested two&lt;/Link&gt;
      &lt;/section&gt;
  )
  }
  
  const HomePage = () =&gt; {
  return(
      &lt;section&gt;
          &lt;h2&gt;This is Home page&lt;/h2&gt;
          &lt;Link to="/about"&gt;About&lt;/Link&gt;
      &lt;/section&gt;
  )
  }
  
  const NestedOne = () =&gt; {
  return (
      &lt;section&gt;
          &lt;h2&gt;Nested page 1&lt;/h2&gt;
      &lt;/section&gt;
  )
  }
  
  
  const NestedTwo = () =&gt; {
  return (
      &lt;section&gt;
          &lt;h2&gt;Nested page 2&lt;/h2&gt;
      &lt;/section&gt;
  )
  }
  
  
   ReactDOM.render(
   &lt;Router&gt; 
    &lt;section&gt;
      &lt;Route exact path="/" component={HomePage} /&gt;
      &lt;Route path="/about" component={AboutPage} /&gt;
      &lt;Route path="/about/nestedone" component={NestedOne} /&gt;
      &lt;Route path="/about/nestedtwo" component={NestedTwo} /&gt;
   &lt;/section&gt;
   &lt;/Router&gt;,
    document.getElementById('root')
  );
  </code></pre>
  
  <p>When I browse <code>/about</code>, I am getting this error:  </p>
  
  <blockquote>
    <p>"Warning: Unknown prop <code>activeClassName</code> on  tag. Remove this prop from the element.</p>
  </blockquote>
  
  <p>What am I doing wrong here?</p>
  
  <p>Thanks!</p>