anchor.diff:  RegExp alphanumeric = new RegExp(r'^[a-zA-Z0-9]+$');
   RegExp numeric = new RegExp(r'^-?[0-9]+$');
   RegExp _int = new RegExp(r'^(?:-?(?:0|[1-9][0-9]*))$');
  -RegExp float = new RegExp(r'^(?:-?(?:[0-9]+))?(?:\.[0-9]*)?(?:[eE][\+\-]?(?:[0-9]+))?$');
  +RegExp _float = new RegExp(r'^(?:-?(?:[0-9]+))?(?:\.[0-9]*)?(?:[eE][\+\-]?(?:[0-9]+))?$');
   RegExp hexadecimal = new RegExp(r'^[0-9a-fA-F]+$');
   RegExp hexcolor = new RegExp(r'^#?([0-9a-fA-F]{3}|[0-9a-fA-F]{6})$');
   
  
positive.code: bool isUppercase(String str) {
    return str == str.toUpperCase();
  }
  
negative.code: 
  // check if the string is a float
  bool isFloat(String str) {
    return _float.hasMatch(str);
  }
  
  
  