Actually getting Lectora to publish HTML5

So I was quite excited to see, in the new features of X.4, that Lectora can publish to HTML5. Or at least, that's what the website (and clearly all of the press releases that people have put on their blogs) says, but for the life of me I can't work out how to actually get it to produce HTML5. Publishing to HTML doesn't have a "HTML5" option, and I can't find one anywhere else, and when you publish to HTML it produces HTML4 transitional (I won't ask about how hard it would be to produce XHTML Strict, because I'm guessing that's still some way from being on the cards). Am I missing some option, or have I misunderstood what exactly is being produced?

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