Unknown tag warning won't go away in Eclipse.

Hello.

I applied the site mesh to the web app, but there is a warning that there are no related tags.

I can guess that this is a warning because there is no sitemesh in HTML DTD Anyway, I tried to remove the warning by modifying the settings on the Eclipse validator side. Like below:

But to no avail. I keep getting warnings. I don't want to use a way to change the settings to ignore "Unknown tag name" globally. Is there any other way?