code: function updateMetrics() {
  
  		isVwDirty = false;
  		DPR = window.devicePixelRatio;
  		cssCache = {};
  		sizeLengthCache = {};
  
  		pf.DPR = DPR || 1;
  
  		units.width = Math.max(window.innerWidth || 0, docElem.clientWidth);
  		units.height = Math.max(window.innerHeight || 0, docElem.clientHeight);
  
  		units.vw = units.width / 100;
  		units.vh = units.height / 100;
  
  		evalId = [ units.height, units.width, DPR ].join("-");
  
  		units.em = pf.getEmValue();
  		units.rem = units.em;
  	}
docs: updates the internal vW property with the current viewport width in px