`body` in `foreignObject` is invalid

<!DOCTYPE html>
<head>
  <title>Awesome page title</title>
</head>
<body>
  
  
  <svg width="400px" height="300px" viewBox="0 0 400 300"
       xmlns="https://www.w3.org/2000/svg">
    <desc>This example uses the 'switch' element to provide a 
          fallback graphical representation of a paragraph, if 
          XHTML is not supported.</desc>

<switch>

<foreignObject width="100" height="50"
                     requiredExtensions="https://www.w3.org/1999/xhtml">
        
        <body xmlns="https://www.w3.org/1999/xhtml">
          <p>Here is a paragraph that requires word wrap</p>
        </body>
      </foreignObject>

<text font-size="10" font-family="Verdana">
        <tspan x="10" y="10">Here is a paragraph that</tspan>
        <tspan x="10" y="20">requires word wrap.</tspan>
      </text>
    </switch>
  </svg>
</body>