@Override
  public @Nls String fetchExternalDocumentation(Project project, PsiElement element, List<String> docUrls, boolean onHover) {
    for (DocumentationProvider provider : getAllProviders()) {
      if (provider instanceof ExternalDocumentationProvider) {
        final String doc = ((ExternalDocumentationProvider)provider).fetchExternalDocumentation(project, element, docUrls, onHover);
        if (doc != null) {
          LOG.debug("fetchExternalDocumentation: ", provider);
          return doc;
        }
      }
    }
    return null;
  }
@Override
  public @Nls String fetchExternalDocumentation(Project project, PsiElement element, List<String> docUrls, boolean onHover)