HtmlArea is a html editing widget which is part of the framework. This widget is available as low-level and UI-level implementation. The first targets traditional webpages / single-page applications and the latter Rich Internet Applications (RIA) as preferred usecase.
Here you can find some interesting technical info.
Note
Please keep in mind that the HtmlArea component provides basic HTML editing functionality. It is not a full-blown HTML editor and will not be developed towards it.
One important step is necessary to get the HtmlArea up and running.
Note
If you setup the component without handing the source parameter you have to place a blank.html file next to your applications index.html.
This is necessary due the Same-Origin Policy implemented by most browsers.