set config(c) {
    this.__config = c;
    /**
     * This event is listened for by ValidateMixin. Whenever the validation config has
     * changed, the FormControl will revalidate itself
     */
    this.dispatchEvent(new Event('config-changed'));
  }
The second argument of the constructor, for instance
`new MinLength(3, {getFeedMessage: async () => 'too long'})`.
Will be stored on Validator instance and passed to `execute` function.
@example
```js
 // Store reference to Validator instance
 const myValidatorInstance = new MyValidator(1, {getMessage() => 'x'});
 // Use this instance initially on a FormControl (that uses ValidateMixin)
 render(html`<validatable-element .validators="${[myValidatorInstance]}"></validatable-element>`, document.body);
 // Based on some event, we need to change the param
 myValidatorInstance.config = {getMessage() => 'y'};
```
@property {ValidatorConfig}