title: What type is register from react-hook-form?
body: <p>When using react-hook-form with Typescript, there is a component that sends some props, <code>register</code> being one of them.</p>
  <p>The issue is with its type when declared in an interface:</p>
  <pre><code>export interface MyProps {
    title: string;
    ...
    register: (string | undefined) =&gt; void;
  }
  </code></pre>
  <p>Which is the correct way of declaring <code>register</code> here?</p>
  <p>Also tried with:</p>
  <pre><code>import { RegisterOptions } from 'react-hook-form';
      export interface MyProps {
        title: string;
        ...
        register: RegisterOptions;
      }
  </code></pre>