matches method
Checks whether all elements in items are contained in this collection.
Returns true if every element of items exists in this collection;
otherwise returns false.
Example:
final mySet = {1, 2, 3};
print(mySet.matches([1, 2])); // true
print(mySet.matches([1, 4])); // false
Implementation
bool matches(Iterable<T> items) => every(items.contains);