The linked article plainly explains it: "The main problem with the RSS title element is how to deal with the characters & and <. They have to be encoded at lea

The linked article plainly explains it: "The main problem with the RSS title element is how to deal with the characters & and <. They have to be encoded at least once as a requirement of XML, but for those aggregators that treat titles as HTML, a second level of encoding may be expected in order to comply with HTML." They have to be encoded at least once but do you do it once, or twice? That's the ambiguity.