code: function ( valPx, basePx ) {
      basePx = basePx || {};
  
      var number = valPx.value,
        base = basePx.value || 15;
  
      if ( !isNaN( number ) ) {
        return lib.format( '{0}em /* em-calc output */', number / base );
      }
  
      throw new Error( 'em-calc expects a number!' );
    }
docs: **calc-em** Calculate the "em" value from the given value in pixels. If a base is passed it will
  be assumed to be the font size of the parent container which the calculated "em value" will be relative to
  
  @param {Object} valPx less object with a value property which holds the numeric value. This is the current
  value of the font in px
  @param {Object} basePx less object with a value property which holds the numeric value. This is the size
  of the font of the parent container in px. If not specified 15 will be used by default
  
  @return {String} a string.