using System;

using HtmlAgilityPack;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        string x = @"<svg/onload=alert('XSS')>";

        HtmlDocument doc = new();

        doc.LoadHtml(x);

        doc.DocumentNode.Descendants()

            .Where(node => node.Name == "script")

            .ToList()

            .ForEach(node => node.Remove());

​

        var l = doc.DocumentNode.SelectNodes("//@*[starts-with(local-name(),'on')]");

        if (l != null) {

            foreach(HtmlNode item in doc.DocumentNode.SelectNodes("//@*[starts-with(local-name(),'on')]")) {

                item.Attributes.Where(a => a.Name.StartsWith("on")).ToList().ForEach(a => a.Remove());

            }

        }

        doc.Save(Console.Out);

    }

}

​

public class NodePositions

{

    public NodePositions(HtmlDocument doc)

    {

        AddNode(doc.DocumentNode);

        Nodes.Sort(new NodePositionComparer());

    }

​

    private void AddNode(HtmlNode node)

    {

        Nodes.Add(node);

        foreach (HtmlNode child in node.ChildNodes)

        {

            AddNode(child);

        }

    }

​

    private class NodePositionComparer : IComparer<HtmlNode>

    {

        public int Compare(HtmlNode x, HtmlNode y)

        {

            return x.StreamPosition.CompareTo(y.StreamPosition);

        }

    }

​

    public List<HtmlNode> Nodes = new List<HtmlNode>();

}