1. Create a seam project.
2. Create a new folder <project>/NewWebContent
3. Open .settings/org.eclipse.wst.common.component
4. Add the new web content folder there:

<wb-resource deploy-path="/" source-path="/NewWebContent">
<wb-resource deploy-path="/" source-path="/WebContent" tag="defaultRootSource"/>

5. Save the file.
6. Open components.xml
7. Add the following components there:

<component name="test" class="broken"></component>
<component name="test" class="broken"></component>

8. Save the file.
9. There should be error markers on the components. But now it's not working since Seam Tools don't recognize WebContent folder as a web root.