@Override
      public void visitXmlAttributeValue(@NotNull XmlAttributeValue value) {
        PsiReference[] references = value.getReferences();
        for (PsiReference reference : references) {
          if (reference instanceof SchemaPrefixReference) {
            if (!XML.equals(((SchemaPrefixReference)reference).getNamespacePrefix()) && reference.resolve() == null) {
              holder.registerProblem(reference, XmlAnalysisBundle.message("xml.inspections.unbound.namespace",
                                                                          ((SchemaPrefixReference)reference).getNamespacePrefix()),
                                     ProblemHighlightType.LIKE_UNKNOWN_SYMBOL);
            }
          }
        }
      }
@Override
      public void visitXmlAttributeValue(@NotNull XmlAttributeValue value)