title: webpack `publicPath`, `path` and webpack-dev-server `contentBase` relationship?
body: <p>What's the relationship between them?</p>
  
  <p>After reading <code>webpack</code> docs. I am still not very clear.</p>
  
  <p>I know <code>output.path</code> clearly. </p>
  
  <p>The docs say that <code>webpack-dev-server</code> will serve the <code>bundle</code> files in memory. So, what's the <code>contentBase</code> property meaning?</p>
  
  <p>and what's the relationship with <code>publicPath</code>?</p>