C# Online Compiler | .NET Fiddle

using System;
using System.Collections.Generic;

public interface IOperation
{
	void Apply(HeadingNode node);
	void Apply(AnchorNode node);
}

public class HighlightOperation: IOperation
{
	public void Apply(HeadingNode node)
	{
		Console.WriteLine("Higlighting heading");
	}
	public void Apply(AnchorNode node)
	{
		Console.WriteLine("Higlighting anchor");
	}
}

public class PlainTextOperation: IOperation
{
	public void Apply(HeadingNode node)
	{
		Console.WriteLine("PlainText heading");
	}
	public void Apply(AnchorNode node)
	{
		Console.WriteLine("PlainText anchor");
	}
}

public interface IHtmlNode
{
	void Execute(IOperation operation);
}

public class HeadingNode: IHtmlNode
{
	public void Execute(IOperation operation)
	{
		operation.Apply(this);
	}
}
public class AnchorNode: IHtmlNode
{
	public void Execute(IOperation operation)
	{
		operation.Apply(this);
	}
}

public class HtmlDocument
{
	private List<IHtmlNode> nodes = new List<IHtmlNode>();
	
	public void Add(IHtmlNode node)
	{
		nodes.Add(node);
	}
	
	public void Execute(IOperation operation) {
		foreach(var node in nodes)
		{
			node.Execute(operation);
		}
	}
}
					
public class Program
{
	public static void Main()
	{
		var htmlDocument = new HtmlDocument();
		htmlDocument.Add(new HeadingNode());
		htmlDocument.Add(new AnchorNode());
		htmlDocument.Execute(new HighlightOperation());
		htmlDocument.Execute(new PlainTextOperation());
	}
}

    private List<IHtmlNode> nodes = new List<IHtmlNode>();
 
using System;
using System.Collections.Generic;
​
public interface IOperation
{
    void Apply(HeadingNode node);
    void Apply(AnchorNode node);
}
​
public class HighlightOperation: IOperation
{
    public void Apply(HeadingNode node)
    {
        Console.WriteLine("Higlighting heading");
    }
    public void Apply(AnchorNode node)
    {
        Console.WriteLine("Higlighting anchor");
    }
}
​
public class PlainTextOperation: IOperation
{
    public void Apply(HeadingNode node)

Cached Result

606.00
10,605.00
100,495.00