Hi,
In fact this feature does not exist in Twistpad, the type (syntax highlight) is always recognized via the document extension or by File - New - "File Type".
If your special files had an extension it would simply fill that extension in the .sdf file of HTML, but since it does not have extension, I'm afraid that is not possible at the moment.
Anyway most likely the behavior of Textpad will be implemented, simply change the syntax type in the documents properties dialogs (or something similar)
Thanks,
André Santos Carthago Software Support
http://www.carthagosoft.net