Sam Ruby’s FeedValidator now includes OPML (Outline Processor Markup Language) validation.  The controversy seems to surround the spec.

The Really Simple Validator validates against the spec, as written. The other two validators validate part against the spec, part against Dave’s guidelines and part against something unknown to me. The concern? The guidelines seem to introduce new constraints to the grammar and validating against an unknown seems wrong. Is this OPML 1.1 or 1.2 and where’s the spec? 

Be sure to read the comments.  Sam Ruby chimes in to explain some of the concerns.