code: function extractExpressionValue (css) {
  
      // parse the comment string:
      // /*varValue*/ --> varValue
      const valueRegExp = /(?:\/\*)(.+)(?:\*\/)/;
      const value = css.match(valueRegExp)[1];
  
      if (!value) {
          message('Warning: empty value');
      }
  
      return value;
  }
docs: Parse calculated variable value
  From CSS comment
  @param css
  @returns {*}