title: D3.js: what is 'g' in .append("g") D3.js code?
body: <p>I am new to <code>D3.js</code>, started learning today only</p>
  
  <p>I looked the the <a href="http://bl.ocks.org/mbostock/3887193" rel="noreferrer">donut example</a> and found this code</p>
  
  <pre><code>var svg = d3.select("body").append("svg")
      .attr("width", width)
      .attr("height", height)
    .append("g")
      .attr("transform", "translate(" + width / 2 + "," + height / 2 + ")");
  </code></pre>
  
  <p>I searched for <a href="https://github.com/mbostock/d3/wiki/Selections#wiki-append" rel="noreferrer">documentation</a>, but did not understood what <code>.append("g")</code> is appending</p>
  
  <p>Is it even <code>D3</code> specific?</p>
  
  <p>Looking for guidance here</p>