       "user": Box(["firstName": "Errol", "lastName": "Flynn"]),
       "spy": Box(willRender)
   ]
-  let rendering = template.render(Box(data))!
+  template.render(Box(data))!
 
 The string argument of DidRenderFunction is optional: it is nil if and only if
 the tag could not render because of a rendering error.

          "firstName": "Sean",
          "lastName": "Connery"],
      "awards": ["Academy Award", "BAFTA Awards", "Golden Globes"]]
  let rendering = template.render(Box(data))!

:see: DidRenderFunction
:see: Tag

  template.registerInBaseContext("square", Box(square))

  // Renders "100"
  template.render(Box(["x": 10]))!


The Filter() function comes in various flavors. Each one targets a use case for
