code: function toPx (value, decl, result) {
    value = (typeof value === 'string' && value.indexOf('calc(') !== -1) ? calc(value) : value;
    var parts = /^(\d*\.?\d+)([a-zA-Z%]*)$/.exec(value);
    if (parts !== null) {
      var number = parts[1];
      var unit   = parts[2];
  
      if (unit === 'px' || unit === '') {
        return parseFloat(number);
      }
      else if (unit === 'em' || unit === 'rem') {
        return parseFloat(number) * BASE_FONT_SIZE;
      }
      else if (unit === '%') {
        return (parseFloat(number) / 100) * BASE_FONT_SIZE;
      } else {
        // other units: vw, ex, ch, etc...
        result.warn('Unit cannot be used for conversion, so 16px is used.');
        return BASE_FONT_SIZE;
      }
    } else {
      throw decl.error('Root font-size is invalid', {plugin: 'pixrem'});
    }
  }
docs: Return a unitless pixel value from any root font-size value.