Actually right now codeform prints all whitespace verbatim into the output file. Any tabs, spaces, or newlines in your source file will also be in the output file.
The HTML output format does indeed use <pre></pre> tags. (See the files rules/_html.)
If you wanted to have tabs converted to spaces or vice versa you could either do it yourself with a separate program -- it's quite easy; I think I have at least five programs that do it -- or create rules that look like this:
Note that I don't know if that will work; keywords containing spaces might not match properly. (And codeform isn't on this computer so I can't test it.) It should however and if it doesn't just give me a shout.Code:=keyword <tab>::<space><space><space><space>:# converts tabs to spaces <space><space><space><space>:<tab>:# converts spaces to tabs
Comments are much appreciated.