How to use markup builder as a big string

I've used MarkupBuilder to make an HTML document:

 

htmlOut = new MarkupBuilder();

htmlOut.html() {

    ...

}

 

Now I want to use htmlOut as a big old string, e.g.:

 

x.method(htmlOut);

 

where the method requires a string.

 

I'm missing something obvious here!

 

Gary