code: function() {
  		if ( !this[ 0 ] ) {
  			return;
  		}
  
  		var offsetParent, offset, doc,
  			elem = this[ 0 ],
  			parentOffset = { top: 0, left: 0 };
  
  		// position:fixed elements are offset from the viewport, which itself always has zero offset
  		if ( jQuery.css( elem, "position" ) === "fixed" ) {
  
  			// Assume position:fixed implies availability of getBoundingClientRect
  			offset = elem.getBoundingClientRect();
  
  		} else {
  			offset = this.offset();
  
  			// Account for the *real* offset parent, which can be the document or its root element
  			// when a statically positioned element is identified
  			doc = elem.ownerDocument;
  			offsetParent = elem.offsetParent || doc.documentElement;
  			while ( offsetParent &&
  				( offsetParent === doc.body || offsetParent === doc.documentElement ) &&
  				jQuery.css( offsetParent, "position" ) === "static" ) {
  
  				offsetParent = offsetParent.parentNode;
  			}
  			if ( offsetParent && offsetParent !== elem && offsetParent.nodeType === 1 ) {
  
  				// Incorporate borders into its offset, since they are outside its content origin
  				parentOffset = jQuery( offsetParent ).offset();
  				parentOffset.top += jQuery.css( offsetParent, "borderTopWidth", true );
  				parentOffset.left += jQuery.css( offsetParent, "borderLeftWidth", true );
  			}
  		}
  
  		// Subtract parent offsets and element margins
  		return {
  			top: offset.top - parentOffset.top - jQuery.css( elem, "marginTop", true ),
  			left: offset.left - parentOffset.left - jQuery.css( elem, "marginLeft", true )
  		};
  	}
docs: position() relates an element's margin box to its offset parent's padding box This corresponds to the behavior of CSS absolute positioning