docs: function convertUnit (xUnit, mUnit, mVal) {
  	if (xUnit !== mUnit) {
  		if (mUnit === 'em') {
  			mVal = options.px_em_ratio * mVal;
  		}
  		if (xUnit === 'em') {
  			mVal = mVal/options.px_em_ratio;
  		}
  	}
  
  	return mVal;
  }