Difference between data-ng-model and ng-model in AngularJS

data-prefix.js

// Reference: http://www.concretepage.com/forum/thread?qid=462

/* 
  This is for #1 and #2.
  <div id="userInfo" data-user-name="Anson">Anson</div>
*/

function nativeJS() { // #1
  var userInfo = document.getElementById("userInfo");
  var name = userInfo.getAttribute("data-user-name");
  // Anson
}

function usingJQ() { // #2
  var userInfo = $('div');
  var name = userInfo.data('user-name');
  // Anson
}

/*
  This is for #3.
  <input ng-model="firstName" />
  <input data-ng-model="lastName" /> 
*/

function usingNG() { // #3
  // firstName and lastName both work perfectly.
}