This is a draft "webmaster tip", under work and review by the Quality Assurance Team, and shouldn't be considered as an official tip from W3C while it remains a draft.
You have used a web authoring tool for your site(s), and the HTML validator tell you it's not valid?
Send a bug report to the tool's developers.
If your image editor messed with your graphics, if your spreadsheet software wasn't able to add a column of figures acurately, you would certainly send their software vendors a bug report, wouldn't you?
Same goes with web autoring tools. Web authoring tools which produce invalid HTML (or XHTML, or CSS) markup are broken, and, as a user of these tools, you can help their developers fix them.
The idea is not to complain endlessly about non-compliance of the tool you are using, but rather make the constructive effort of sending acurate reports (along with examples) of wrong behaviours with regards to the web standards.
If users make this effort of sending good bug reports, vendors and developers are more likely to fix their products, and everyone will benefit from good authoring tools which behave correctly with regards to standards.
Here is a (rather incomplete) list of authoring tools with the proper channel to report a bug:
Created Date: 2002-04-18 by Olivier Thereaux