Error: Element ul not allowed as child of element ul in this context. Additionally, this can be verified by the HTML5 spec which lists ul 's possible children as li only. I think I understand why ...

As found out in getpelican/pelican#2895, the generated code for nested, unordered lists fails the html-linter: "48:76: Error: General Formatting: Use a new line for every block, list, or table element ...