anchor.diff:    return version == '6' && ipv6.hasMatch(str);
   }
   
  +
   // check if the string is a fully qualified domain name (e.g. domain.com).
   bool isFQDN(str, [options]) {
     Map default_fqdn_options = {
  
positive.code: 
  }
  
  // check if the string is an IP (version 4 or 6)
  bool isIP(String str, [version]) {
    version = version.toString();
  
negative.code:     }
    }
    return true;
  }
  
  
  // check if the string contains only letters (a-zA-Z).
  bool isAlpha(String str) {
    return alpha.hasMatch(str);
  }
  
  
  // check if the string contains only numbers
  bool isNumeric(String str) {
    return numeric.hasMatch(str);
  }
  
  
  // check if the string contains only letters and numbers
  bool isAlphanumeric(String str) {
    return alphanumeric.hasMatch(str);
  }
  
  
  // check if a string is base64 encoded
  bool isBase64(String str) {
    return base64.hasMatch(str);
  }
  
  
  // check if the string is an integer
  bool isInt(String str) {
    return _int.hasMatch(str);
  }
  
  
  // check if the string is a float
  bool isFloat(String str) {
    return float.hasMatch(str);
  }
  
  
  // check if the string is a hexadecimal number
  bool isHexadecimal(String str) {
    return hexadecimal.hasMatch(str);
  }
  
  
  // check if the string is a hexadecimal color
  bool isHexColor(String str) {
    return hexcolor.hasMatch(str);
  }
  