Sorry, a little late with my reply. It's mostly about removing stuff from HTML - JavaScript, forms, and various CSS features - to make it focus on simple forma

Sorry, a little late with my reply. It's mostly about removing stuff from HTML - JavaScript, forms, and various CSS features - to make it focus on simple formatting. Then requiring the appropriate CSP security constraints to ensure privacy/security. Finally, standardizing on a way to include binary files (images, etc.) in the format using a JSON blob at the end of the text which can be referenced above. Self contained, document focused, cross platform, secure and private, while still being standard HTML. Would replace ePub, .docx, Markdown, and provide a standard file format for Google Docs to export to.