In worldoutline, if you put format=OPML at the end of a URL, we return the OPML for the item instead of the HTML.
However there are problems if what's displayed is a thumblist, which is an indirect nodetype. Its url attribute points to the OPML for the page.
This problem was pointed out in a post to the world-outline list by Karsten Wolf.
If the page was empty it was returning invalid OPML. Karsten reports that the body element was not closed, but that's not all that's wrong. The opml element wasn't closed either. This appears to be a kernel bug and not something I can address at this time.
Karsten also points out that the encoding and version number in the XML header are in the wrong order. Again, this is something that's produced by the kernelized xml.decompile verb. Not something I have any control over at the web-app level.
Luckily this is something that can be fixed. :-)
I just read the OPML from the URL and return that.
This could be extended to other indirect types, but I'll deal with those when they come up as issues.