I have moved your thread out of the Graphics forums into the Web forum.
Please ensure you post to the correct forum to get the best answers.

Xara Xtreme Pro is not a HTML editor.
Forget about tags and all html code. Xara Xtreme is a WYSIWYG graphic designer which outputs to HTML at export time.
There is no HTML code internally while you are designing in Xtreme.

However, one of the great features is 'placeholders'. You can read more about placeholders and how they add functionality in the Xara Xtreme 5 Help file or by doing a search at TG for 'placeholders' - you will get many results, it's a very popular topic.