Raw HTML mode is provided for occasions when it is necessary to insert a completley customised page design. The HTML replaces the entire <body> tag in the template, so it is possible to include just about any page content, including frames.
The body text entry should begin with the address of a stylesheet enclosed in <>, followed by the <body> tag, and ending with the </body> tag.
All the warnings about bad HTML apply even more so to Raw HTML. Since none of the normal 'furniture' is preserved, the user needs to define navigation controls.
Both HTML and Raw HTML modes are designed for occasional use. If you find that you are using either of them on a regular basis, it may be that you would be better off with a classic FTP account.