title: MDI form in C# Parent And Child
body: <p>I have 3 forms on my project.</p>
  
  <ul>
  <li><code>form1</code> is MDI controller</li>
  <li><code>form2</code> and <code>form3</code> are MDI children</li>
  </ul>
  
  <p>How do I create <code>form1</code> as the parent and <code>form2</code> and <code>form3</code> as children?</p>
  
  <p>Something like old MFC's MDI interface:</p>
  
  <p><a href="https://i.stack.imgur.com/nE3Um.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nE3Um.png" alt="enter image description here"></a></p>
  
  <p>Imagine <code>form2</code> is the parent and has a button. If clicked, it must open <code>form3</code> in the parent form (<code>form1</code>).  How do I set this up?</p>