contains static method
Implementation
static Validator<String> contains(String data, {String? error}) => (
value,
context,
) {
final bool contains = context.caseHandling == CaseHandling.ignore
? value.toLowerCase().contains(data.toLowerCase())
: value.contains(data);
if (contains) return (true, null);
return (false, error ?? context.errors.stringErrors.contains(data));
};