It would also be extremely helpful to have a way to preview the different output formats so we can test our finished HTML and make sure it works properly not only as HTML but also as the source for the other formats.
This could be so difficult as to be nigh on impossible. For example, as most here know, the ".epub" format is actually just a zip file containing (among other things) the XHTML version of the document....
Sorry, but I've looked and tried to port Marcello's HTML->epub code and its anything but that simple. (But I am not an experienced Python coder) Again, to my mind a "preview" need simply be a portable version of Marcello's code so that we can do our own HTML to ePub conversion (and from there to MOBI) and run it on the variety of ePub and MOBI reader devices and software we already own, so that we have *some* idea of the problems that the particular HTML is going to run into on various portable devices. And I am sure there are any number of people who are willing to preview a DP candidate release on the hardware they own in order to find what problems there are to be found -- most of us are pretty passionate about our choice of hardware and would like very much for DP/PG to produce ebooks that actually work on our hardware investments! PS: I already to make preview versions of my HTML on ePub and MOBI -- its just that the HTML->ePub and HTML->MOBI conversion software I have is not identical to Marcello's and thus the formatting ends up different than the "official" version.