First, check the Web authoring frequently asked questions (FAQs) to see if your question has been answered there.
If it hasn't, you can send it to one of the following forums:
Each of these forums have plenty of experienced HTML authors who are willing to share their expertise. (If you are commenting on a specific page, be sure to provide a URL when you ask your question!)
Please join and contribute to the www-validator
mailing list.
If you just have a small patch and don't want to join the list, feel free to send it directly to the list.
You can send me e-mail, and I will try to respond as soon as I can. I'm sorry that I may not be able to reply to every message I receive.
Please try to use one of the online forums mentioned above; much of the time others will be able to help, and having the discussion in an open publicly-archived forum has many other benefits as well.