Markdig checklist extension

ChecklistExtension.cs

public class ChecklistExtension : IMarkdownExtension
{
    public void Setup(MarkdownPipelineBuilder pipeline)
    {
        if (pipeline.InlineParsers.Contains<TaskListInlineParser>())
            return;

        if (pipeline.InlineParsers.Contains<ChecklistInlineParser>())
            return;

        // Insert the parser after the code span parser
        var checklistInlineParser = new ChecklistInlineParser();
        pipeline.InlineParsers.InsertBefore<LinkInlineParser>(checklistInlineParser);
    }

    public void Setup(MarkdownPipeline pipeline, IMarkdownRenderer renderer)
    {
        var htmlRenderer = renderer as HtmlRenderer;
        if (htmlRenderer != null)
        {
            htmlRenderer.ObjectRenderers.AddIfNotAlready<HtmlChecklistItemRenderer>();
        }

        var normalizeRenderer = renderer as NormalizeRenderer;
        if (normalizeRenderer != null)
        {
            normalizeRenderer.ObjectRenderers.AddIfNotAlready<NormalizeTaskListRenderer>();
        }
    }
}

ChecklistInlineParser.cs

public class ChecklistInlineParser : TaskListInlineParser
{
    public override bool Match(InlineProcessor processor, ref StringSlice slice)
    {
        bool match = base.Match(processor, ref slice);

        if (match)
        {
            var listItemBlock = (ListItemBlock) processor.Block.Parent;
            var listBlock = (ListBlock) listItemBlock.Parent;
            var taskList = (TaskList) processor.Inline;
            processor.Inline = new ChecklistItem(taskList, listBlock.Line, listItemBlock.Line);
        }

        return match;
    }
}

ChecklistItem.cs

public class ChecklistItem : LeafInline
{
    private readonly TaskList taskList;

    public ChecklistItem(TaskList taskList, int listBlockLineNumber, int listItemLineNumber)
    {
        this.taskList = taskList ?? throw new ArgumentNullException(nameof(taskList));
        Id = $"checklist-{listBlockLineNumber}-item-{listItemLineNumber}";
    }

    public bool Checked => this.taskList.Checked;

    public string Id { get; }
}

Main.cs

var checklistExtension = new ChecklistExtension();
var pipelineBuilder = new MarkdownPipelineBuilder();
pipelineBuilder.Extensions.Add(checklistExtension);
pipelineBuilder.DisableHtml();
var pipeline = pipelineBuilder.Build();

using (var stringWriter = new StringWriter())
{
    var document = Markdown.ToHtml("…", stringWriter, pipeline);
    var html = stringWriter.ToString();
    // How do I get to the leaf nodes within 'document'?
}