I was fixing a bug in OmniOutliner where it wouldn't open a file with an uppercase .OPML suffix. I did some digging, and the fix was to register the app as handling the com.apple.news.opml file type.
... Brent Simmons writing on his blog about OPML.
In the short piece, he references Dave Winer, the inventor of OPML. Why is this interesting?
Well I use Omni Outliner and I use some of Dave Winer's software - including this blog that you are now reading.
OPML is used for aspects of this site and the river site I run here.
Time to do some investigation because I rarely find OPML files created by OmniOutliner play happily with Dave's world. I have always put it down to operator (that would me) error. Now, I am not so sure.