<https://productled.com/how-to-decide-what-features-you-should-give-away-for-free-vs-which-ones-to-gate/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://productled.storychief.io/how-to-decide-what-features-you-should-give-away-for-free-vs-which-ones-to-gate>