code: function setFixed() {
              // Only fix the target element and the spacer if we need to.
              if (!isFixed()) {
                  //get REAL dimensions (decimal fix)
                  //Ref. http://stackoverflow.com/questions/3603065/how-to-make-jquery-to-not-round-value-returned-by-width
                  var dimensions = target[0].getBoundingClientRect();
  
                  // Set the spacer to fill the height and width of the target
                  // element, then display it.
                  spacer.css({
                      'display' : target.css('display'),
                      'width' : dimensions.width,
                      'height' : dimensions.height,
                      'float' : target.css('float')
                  });
  
                  // Set the target element to fixed and set its width so it does
                  // not fill the rest of the page horizontally. Also, set its top
                  // to the margin top specified in the options.
  
                  cssOptions={
                      'z-index' : base.options.zIndex,
                      'position' : 'fixed',
                      'top' : base.options.bottom == -1?getMarginTop():'',
                      'bottom' : base.options.bottom == -1?'':base.options.bottom,
                      'margin-left' : '0px'
                  }
                  if (!base.options.dontSetWidth){ cssOptions['width']=target.css('width'); };
  
                  target.css(cssOptions);
  
                  target.addClass(base.options.baseClassName);
  
                  if (base.options.className) {
                      target.addClass(base.options.className);
                  }
  
                  position = 'fixed';
              }
          }
docs: Sets the target element to fixed. Also, sets the spacer to fill the void left by the target element.