code: function (content) {
    if (content === null)
      throw new Error("Can't render null");
    if (typeof content === 'undefined')
      throw new Error("Can't render undefined");
  
    if ((content instanceof Blaze.View) ||
        (content instanceof Blaze.Template) ||
        (typeof content === 'function'))
      return;
  
    try {
      // Throw if content doesn't look like HTMLJS at the top level
      // (i.e. verify that this is an HTML.Tag, or an array,
      // or a primitive, etc.)
      (new HTML.Visitor).visit(content);
    } catch (e) {
      // Make error message suitable for public API
      throw new Error("Expected Template or View");
    }
  }
docs: Blaze.render publicly takes a View or a Template. Privately, it takes any HTMLJS (extended with Views and Templates) except null or undefined, or a function that returns any extended HTMLJS.