# toggle method

bool toggle (String value, [ bool shouldAdd ])

Adds the class `value` to the element if it is not on it, removes it if it is.

If `shouldAdd` is true, then we always add that `value` to the element. If `shouldAdd` is false then we always remove `value` from the element.

## Implementation

    bool toggle(String value, [bool shouldAdd]) {
      _validateToken(value);
      Set<String> s = readClasses();
      bool result = false;
      if (shouldAdd == null) shouldAdd = !s.contains(value);
      if (shouldAdd) {
        s.add(value);
        result = true;
      } else {
        s.remove(value);
      }
      writeClasses(s);
      return result;
    }