When you nest a comment, replace "--" with "- -". When you un-nest, reverse the procedure. It's not the <!-- that is forbidden but the --.

When you nest a comment, replace "--" with "- -". When you un-nest, reverse the procedure. It's not the <!-- that is forbidden but the --.

Example:

<!-- some stuff <!- - some inner stuff - -> <!- - a sibling - -> the footer -->