> Some well-formedness rules may have to be more carefully checked in
> translations. But other than this it should work pretty well.

I fail to see the general usefulness of conversion between formats if 
only a subset of the capabilities can be converted. If my document 
written in Textile relies on footnotes then a lossy conversion to RDoc 
without the footnotes would make little sense. The lossy conversion 
leads to a corrupt product.

That is unless someone would go about bringing all the markup languages 
up to the _highest_ common denominator (HCD) -- either by direct 
alteration of the language or by work-arounds (representing footnotes 
in RDoc in parenteses behind the referenced word or sentence).

But all this is missing the point. The reason different markup 
languages exist is to cater for different applications. Textile is good 
for integrating with HTML (thanks to CSS hooks among other things), 
RDoc is already the language for documenting Ruby code.

If conversions are to work to the HCD, then the differences between the 
languages are reduced to somewhat meaningless syntaxes.

Anyway, this seems to be a much more philosophical than pragmatic 
discussion. The usage benefit of switching between markup languages on 
the fly seems incredibly small compared to the amount of work required 
to convert at the HCD.

But I am in no way going to argue or refuse a patch from someone 
committed to keep all supported markup languages supported by a HCD 
approach. Bring it on! :)
--
David Heinemeier Hansson,
http://www.instiki.org/      -- A No-Step-Three Wiki in Ruby
http://www.basecamphq.com/   -- Web-based Project Management
http://www.loudthinking.com/ -- Broadcasting Brain
http://www.nextangle.com/    -- Development & Consulting Services