How can i create a word header from a html string

Question

I'm generating a word docx file from a html string and using various articles I've found how to add simple headers and footers to that document. What I now need to do is generate the header from a html string too but I'm struggling to find an example of how this is done. The author of this question: Export docx/doc First Header and Footer as docx File Using openXML says he has done it but unfortunately he hasn't posted an example.

My code below successfully adds a header but as you can see from the code it will only add the html as text in the header, whereas I want to pass in a html string and that to appear in the header as formatted html.

Has anyone done this?

static void AddHeaderPart(MainDocumentPart mainPart, string headerHtml, Encoding encoding)
        {
            if (mainPart == null || string.IsNullOrEmpty(headerHtml))
            {return;}

            // Create a new header part.
            HeaderPart headerPart = mainPart.AddNewPart<HeaderPart>();

            // Get Id of the headerPart.
            string rId = mainPart.GetIdOfPart(headerPart);


            // Call GenerateHeaderPartContent
            GenerateHeaderPartContent(mainPart, headerPart, headerHtml, encoding);

            // Get SectionProperties and Replace HeaderReference with new Id.
            IEnumerable<SectionProperties> sectPrs = mainPart.Document.Body.Elements<SectionProperties>();
            foreach (var sectPr in sectPrs)
            {
                // Delete existing references to headers.
                sectPr.RemoveAllChildren<HeaderReference>();

                // Create the new header reference node.
                sectPr.PrependChild<HeaderReference>(new HeaderReference() { Id = rId, Type = HeaderFooterValues.Default });
            }

        }

static void GenerateHeaderPartContent(MainDocumentPart mainPart, HeaderPart headerPart, string headerHtml, Encoding encoding)
        {
            Header header1 = new Header() { MCAttributes = new MarkupCompatibilityAttributes() { Ignorable = "w14 wp14" } };
            header1.AddNamespaceDeclaration("wpc", "http://schemas.microsoft.com/office/word/2010/wordprocessingCanvas");
            header1.AddNamespaceDeclaration("mc", "http://schemas.openxmlformats.org/markup-compatibility/2006");
            header1.AddNamespaceDeclaration("o", "urn:schemas-microsoft-com:office:office");
            header1.AddNamespaceDeclaration("r", "http://schemas.openxmlformats.org/officeDocument/2006/relationships");
            header1.AddNamespaceDeclaration("m", "http://schemas.openxmlformats.org/officeDocument/2006/math");
            header1.AddNamespaceDeclaration("v", "urn:schemas-microsoft-com:vml");
            header1.AddNamespaceDeclaration("wp14", "http://schemas.microsoft.com/office/word/2010/wordprocessingDrawing");
            header1.AddNamespaceDeclaration("wp", "http://schemas.openxmlformats.org/drawingml/2006/wordprocessingDrawing");
            header1.AddNamespaceDeclaration("w10", "urn:schemas-microsoft-com:office:word");
            header1.AddNamespaceDeclaration("w", "http://schemas.openxmlformats.org/wordprocessingml/2006/main");
            header1.AddNamespaceDeclaration("w14", "http://schemas.microsoft.com/office/word/2010/wordml");
            header1.AddNamespaceDeclaration("wpg", "http://schemas.microsoft.com/office/word/2010/wordprocessingGroup");
            header1.AddNamespaceDeclaration("wpi", "http://schemas.microsoft.com/office/word/2010/wordprocessingInk");
            header1.AddNamespaceDeclaration("wne", "http://schemas.microsoft.com/office/word/2006/wordml");
            header1.AddNamespaceDeclaration("wps", "http://schemas.microsoft.com/office/word/2010/wordprocessingShape");

            Paragraph paragraph1 = new Paragraph();

            ParagraphProperties paragraphProperties1 = new ParagraphProperties();
            ParagraphStyleId paragraphStyleId1 = new ParagraphStyleId() { Val = "Header" };

            paragraphProperties1.Append(paragraphStyleId1);

            //This adds the headerHtml as text - how to add it as html?
            Run run1 = new Run();
            Text text1 = new Text();
            text1.Text = headerHtml;

            run1.Append(text1);

            paragraph1.Append(paragraphProperties1);
            paragraph1.Append(run1);

            header1.Append(paragraph1);

            headerPart.Header = header1;
        }

Answer 1

So the code below uses an altChunk to add html into the header. It's not perfect as I get validation errors when I use the OpenXmlValidator to validate the generated document although the doc still opens ok in word but I'm posting it here as an answer as it does do what I asked above & it might help others:

static void GenerateHeaderPartContent(MainDocumentPart mainPart, HeaderPart headerPart, string headerHtml)
        {
            Header header1 = new Header() { MCAttributes = new MarkupCompatibilityAttributes() { Ignorable = "w14 wp14" } };
            header1.AddNamespaceDeclaration("wpc", "http://schemas.microsoft.com/office/word/2010/wordprocessingCanvas");
            header1.AddNamespaceDeclaration("mc", "http://schemas.openxmlformats.org/markup-compatibility/2006");
            header1.AddNamespaceDeclaration("o", "urn:schemas-microsoft-com:office:office");
            header1.AddNamespaceDeclaration("r", "http://schemas.openxmlformats.org/officeDocument/2006/relationships");
            header1.AddNamespaceDeclaration("m", "http://schemas.openxmlformats.org/officeDocument/2006/math");
            header1.AddNamespaceDeclaration("v", "urn:schemas-microsoft-com:vml");
            header1.AddNamespaceDeclaration("wp14", "http://schemas.microsoft.com/office/word/2010/wordprocessingDrawing");
            header1.AddNamespaceDeclaration("wp", "http://schemas.openxmlformats.org/drawingml/2006/wordprocessingDrawing");
            header1.AddNamespaceDeclaration("w10", "urn:schemas-microsoft-com:office:word");
            header1.AddNamespaceDeclaration("w", "http://schemas.openxmlformats.org/wordprocessingml/2006/main");
            header1.AddNamespaceDeclaration("w14", "http://schemas.microsoft.com/office/word/2010/wordml");
            header1.AddNamespaceDeclaration("wpg", "http://schemas.microsoft.com/office/word/2010/wordprocessingGroup");
            header1.AddNamespaceDeclaration("wpi", "http://schemas.microsoft.com/office/word/2010/wordprocessingInk");
            header1.AddNamespaceDeclaration("wne", "http://schemas.microsoft.com/office/word/2006/wordml");
            header1.AddNamespaceDeclaration("wps", "http://schemas.microsoft.com/office/word/2010/wordprocessingShape");

            Paragraph paragraph1 = new Paragraph();
            ParagraphProperties paragraphProperties1 = new ParagraphProperties();
            ParagraphStyleId paragraphStyleId1 = new ParagraphStyleId() { Val = "Header" };

            paragraphProperties1.Append(paragraphStyleId1);
            paragraph1.Append(paragraphProperties1);

            string altChunkId = "AltChunkId1";
            AlternativeFormatImportPart chunk = headerPart.AddAlternativeFormatImportPart(
                AlternativeFormatImportPartType.Html, altChunkId);

            // Note that headerHtml should be full html, not just a snippet
            // eg. <html><h1>My Header</h1></html> is OK
            // <h1>My Header</h1> is not OK
            MemoryStream ms = new MemoryStream(new UTF8Encoding(true).GetPreamble().Concat(Encoding.UTF8.GetBytes(headerHtml)).ToArray());

            chunk.FeedData(ms);

            AltChunk altChunk = new AltChunk();
            altChunk.Id = altChunkId;

            Run run1 = new Run();
            RunProperties runProps = new RunProperties();
            NoProof noProof1 = new NoProof();
            runProps.Append(noProof1);

            run1.Append(runProps);
            run1.Append(altChunk);

            paragraph1.Append(run1);
            header1.Append(paragraph1);

            headerPart.Header = header1;
        }