Extending

v5 converts each HTML tag with an IConverter. You can register your own converter for any tag, or alias one tag to another.

Alias one tag to another

The quickest customization is to reuse an existing tag's converter. For example, to convert <u> like <em>:

var converter = new ReverseMarkdown.Converter();
converter.Register("u", new ReverseMarkdown.Converters.AliasConverter(converter, "em"));

The same effect is available declaratively via the TagAliases option:

var config = new ReverseMarkdown.Config();
config.TagAliases["u"] = "em";

var converter = new ReverseMarkdown.Converter(config);

Wrap an unknown tag

To wrap an unknown tag's content with markdown without writing a converter, use UnknownTagsReplacer:

var config = new ReverseMarkdown.Config();
config.UnknownTagsReplacer["u"] = "*"; // <u>text</u> -> *text*

var converter = new ReverseMarkdown.Converter(config);

Custom converter

For full control, implement IConverter and register it against a tag name. The interface writes to a TextWriter:

public interface IConverter
{
    void Convert(TextWriter writer, HtmlNode node);
}

Deriving from ConverterBase gives you access to the owning Converter and helpers such as TreatChildrenAsString(node):

using System.IO;
using HtmlAgilityPack;
using ReverseMarkdown;
using ReverseMarkdown.Converters;

public sealed class HighlightConverter : ConverterBase
{
    public HighlightConverter(Converter converter) : base(converter)
    {
        // Register this converter for the <mark> tag.
        Converter.Register("mark", this);
    }

    public override void Convert(TextWriter writer, HtmlNode node)
    {
        writer.Write("==");
        writer.Write(TreatChildrenAsString(node));
        writer.Write("==");
    }
}

var converter = new ReverseMarkdown.Converter();
_ = new HighlightConverter(converter);

var result = converter.Convert("<mark>important</mark>");
// ==important==

You can also register a converter directly without deriving from ConverterBase, as long as it implements IConverter:

converter.Register("mark", new HighlightConverter(converter));

v6 changed the extension model

v6 replaced the IConverter / HtmlNode model with a reader/writer model over a Markdown DOM (IMdReader + [MarkdownReader], and Parse/Render). Custom v5 converters do not carry over. See the v6 extending guide.