Bloom.Book.HtmlDom.EnsureIdsAreUnique C# (CSharp) Method

        private static void EnsureIdsAreUnique(HtmlDom dom, string elementTag, List<string> ids, StringBuilder builder)
        {
            foreach(XmlElement element in dom.SafeSelectNodes("//" + elementTag + "[@id]"))
            {
                var id = element.GetAttribute("id");
                if(ids.Contains(id))
                    builder.AppendLine("The id of this " + elementTag + " must be unique, but is not: " + element.OuterXml);
                else
                    ids.Add(id);
            }
        }