Lotus Notes/Domino has supported HTML and pass-through HTML for ages, and now in Domino 6 there are new features for editing and rendering HTML.
With Domino Designer 6 you can add a new pane into the Designer client—the HTML Pane. To enable this new pane, you need to have some HTML on your form/page. Without HTML, there is no point having an HTML Pane available, so this new menu and feature element is context sensitive.
Context sensitive means that elements are available only from where they should be available. For the HTML Pane, this means that you will not be able to enable this pane unless you are in a form or page, and that you in fact are currently inside a pass-through HTML text.