private static boolean isPropertyKey(@NotNull PsiElement element) {
    PsiElement sibling = element.getParent(); // element is leaf, parent is reference expression
    while ((sibling = sibling.getPrevSibling()) != null) {
      if (":".equals(sibling.getText())) return false; // no completion for values
    }
    return true;
  }
private static boolean isPropertyKey(@NotNull PsiElement element)