title: jQuery underscore notation
body: <p>Could anybody give me an explanation of the underscore in a jQuery plugin function? I have no idea of what "<em>_</em>" means. Example code below:</p>
  
  <pre><code>$.fn.bgStretch=function(o){
      this.each(function(){
          var th=$(this),
              data=th.data('bgStretch'),
              _={
                  align:'leftTop',
                  altCSS:{},
                  css:{
                      leftTop:{
                          left:0,
                          right:'auto',
                          top:0,
                          bottom:'auto'
                      },
                      rightTop:{
                          left:'auto',
                          right:0,
                          top:0,
                          bottom:'auto'
                      },
                      leftBottom:{
                          left:0,
                          right:'auto',
                          top:'auto',
                          bottom:0
                      },
                      rightBottom:{
                          left:'auto',
                          right:0,
                          top:'auto',
                          bottom:0
                      }
                  },
                  preFu:function(){
                      _.img
                          .load(function(){
                              _.checkWidthFu()
                              _.img
  </code></pre>