This “view” is the main component for displaying HTML content. It can be used in various situations such as e-mail reader programs or as the JavaHelp renderer.
The Browser has an option to offer WYSIWYG editing of the content which makes real e-mail applications possible.
The HTML source code is displayed with color highlights to make it easier to read. You can not only use copy actions on the code but also paste.
The API has an option to enable applying the modified source code to the viewer. So you could edit your HTML via WYSIWYG and in the code - e.g. to add some CSS styles.