code: function () {
              var cfg = this.cfg,
                  fc = cfg.getProperty("fixedcenter");
  
              if (cfg.getProperty("visible")) {
                  if (fc && (fc !== _CONTAINED || this.fitsInViewport())) {
                      this.center();
                  }
              }
          }
docs: Fixed center event handler used for centering on scroll/resize, but only if
  the overlay is visible and, if "fixedcenter" is set to "contained", only if
  the overlay fits within the viewport.
  
  @method doCenterOnDOMEvent