isIn method
Check if the string is in an array of allowed values
Implementation
bool isIn(Object? values) {
var str = this;
if (values == null) return false;
if (values is String) {
return values.contains(str);
}
if (values is! Iterable) return false;
for (Object? value in values) {
if (value.toString() == str) return true;
}
return false;
}