A doc template uses tags to delimit dynamic sections in the document. To open the assistant with MDWorkbench, click Window > Open Doc Template Assistant.

The top pane lists the tags elements which can be used in the document. You can drag a tag from this list and drop it into your Document Authoring tool. This allows quick writing of your document.
Note that Scripts view and Models view are available in this assitant, and support textual drag & drop to compose a doc template.
Let's change the doc template static contents:
[#parameters]in model : uml21[/#parameters]
[#file]result.xml[/#file]
Introduction
This document is generated using MDWorkbench.
Note: apply the style Heading 1 to "Introduction".
We will now insert a comment tag in our document. The comment tag enables to insert a description in the doc template that won't be part of the generated document. The contents of the comment is informative and is ignored by the doc template generation engine.
The doc template contents should now be:
[#parameters]in model : uml21[/#parameters]
[#file]result.xml[/#file]
Introduction
This document is generated using MDWorkbench.
[#comment]This is a comment, not part of the output[/#comment]