title: Simulink: Add custom property to a block
body: <p>I would like to add a new property to a selected block.</p>
  
  <p>For example, when i write </p>
  
  <pre><code>get_param(gcb,'ObjectParameters')
  </code></pre>
  
  <p>I would like to see my custom property.</p>
  
  <p>I tried the command <code>add_param</code> but without success.</p>
  
  <pre><code>add_param(gcb,'Foo','foo')
  Input argument 1 must be a block diagram
  </code></pre>