code: function ( valPx, basePx ) {
      basePx = basePx || { value: 15 };
      if ( !isNaN( valPx.value ) ) {
        return valPx.value / basePx.value + 'em';
      }
      throw new Error( 'calc-em 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.