Using text-indent with animate

Using text-indent with animate

Following a JQuery tutorial, the instructor uses this code to rotate a menu button

  1. $('#toggleMenu').animate({
  2.     'text-indent':1
  3. },{
  4.     duration:1000,
  5.     easing:'linear',
  6.     step:function(now){
  7.         $(this).css('transform', rortateZ(' + (now * 360) + 'deg)');   
  8.     }
  9. });

And then same code but with 'text-indent':0 to reverse the animation, the instructor said he is using 'text-indent' to be used with step function but I really dont understand, can you explain more the what is the role of 'text-indent' in this animation ?