Simpler Hello World

Here is the simplest Hello World, according to jump start:
http://jumpstart.doublenegative.com.au/jumpstart/helloworld

I would like to do something simpler.  No html, body tags etc, just pure streaming content.  Comlpletely do away with templates and components, just use the page
class to stream "Hello World" to browser.

In above example, I tried to set HelloWorld.tml as just

${username}

the idea being getUserName can be XML, PDF or whatever...but get the following error:

  Content is not allowed in prolog