1) use https://issues.jboss.org/browse/JBIDE-10173 as example project;
2) add org.jboss.tools.jsf.jsfnature and org.jboss.tools.jst.web.kb.kbnature to the project;
3) open stopka-ui-test\src\main\webapp\test.jspx in VPE;
4) use Ctlr+LMouse click on <stopka:css> to open corresponding tld file;
5) stopka.tld is opened;
6) move the mouse over the editor - and you will get:
Unexpected runtime error while computing a text hover
java.lang.NullPointerException
at org.jboss.tools.common.el.core.resolver.ELResolverFactoryManager.getResolvers(ELResolverFactoryManager.java:105)
at org.jboss.tools.jst.web.kb.PageContextFactory.createPageContext(PageContextFactory.java:418)
at org.jboss.tools.jst.web.kb.PageContextFactory.createPageContext(PageContextFactory.java:231)
at org.jboss.tools.jst.web.kb.PageContextFactory.createPageContext(PageContextFactory.java:198)
at org.jboss.tools.jst.web.kb.PageContextFactory.createPageContext(PageContextFactory.java:187)
at org.jboss.tools.jst.jsp.jspeditor.info.FaceletTagInfoHoverProcessor.computeHoverHelp(FaceletTagInfoHoverProcessor.java:91)
at org.eclipse.wst.xml.ui.internal.taginfo.XMLTagInfoHoverProcessor.getHoverInfo(XMLTagInfoHoverProcessor.java:257)
at org.jboss.tools.common.text.xml.info.ChainTextHover.getHoverInfo2(ChainTextHover.java:145)
at org.eclipse.jface.text.TextViewerHoverManager$4.run(TextViewerHoverManager.java:166)