docs: public static Matcher<ClassTree> nestingKind(final NestingKind kind) {
      return new Matcher<ClassTree>() {
        @Override
        public boolean matches(ClassTree classTree, VisitorState state) {
          ClassSymbol sym = ASTHelpers.getSymbol(classTree);
          return sym.getNestingKind() == kind;
        }
      };
    }