Thanks for your reply.
I am sorry that there is conflicting information. This is an outdated help page and I have submitted a request to have the erroneous information removed. The help page I provided in my first post has the most up-to-date help page.
In relation to the other seller, the detail page was created before these rules were imposed.
If you do try to use HTML coding on product detail pages we cannot guarantee that it will always work. We will also be unable to troubleshoot any HTML issues you may experience on product detail pages. We have found that information does not display correctly on mobile devices if HTML is present.
If there is any change to this rule there will be a notification in your Seller Central Homepage headlines section.