h5p.json got, according to H5P specifications, the following properties:
title, language, machineName, preloadedDependencies, embedTypes
contentType, description, author, license, dynamicDependencies, width, height, metaKeywords, metaDescription
But I got the following error if I does not have mainLibrary defined:
"The required property mainLibrary is missing from h5p.json"
(By the way, the example Boardgame does not have this property..)