Example to search Episerver blocks in XhtmlString properties, requires Vulcan.Core > 3.x

CustomIndexModifier.cs

using System.Collections.Generic;
using System.Linq;
using EPiServer.Core;
using EPiServer.Core.Html.StringParsing;
using EPiServer.Security;
using EPiServer.ServiceLocation;
using TcbInternetSolutions.Vulcan.Core;
using TcbInternetSolutions.Vulcan.Core.Extensions;

namespace WSOL.Web.Business.Vulcan
{
    [ServiceConfiguration(typeof(IVulcanIndexingModifier), Lifecycle = ServiceInstanceScope.Singleton)]
    public class CustomIndexModifier : IVulcanIndexingModifier
    {
        public void ProcessContent(IVulcanIndexingModifierArgs args)
        {            
            var contents = new List<string>();
            var properties = args.Content.GetType().GetProperties();

            foreach (var p in properties)
            {
                // Property to string conversions
                if (p.PropertyType != typeof(XhtmlString)) continue;

                var value = p.GetValue(args.Content);
                var references = GetStringReferences(value as XhtmlString);
                var searchArea = new ContentArea();

                foreach(var reference in references)
                    searchArea.Items.Add(new ContentAreaItem(reference));
                    

                contents.Add(searchArea.GetContentAreaContents());
            }

            if (contents.Count == 0) return;
            var stringContents = string.Join(separator: " ", values: contents);
            if (string.IsNullOrWhiteSpace(stringContents)) return;

            args.AdditionalItems["__xhtmlStringSearchContents"] =  stringContents;
        }

        // https://world.episerver.com/blogs/Per-Magne-Skuseth/Dates/2016/1/episerver-find-index-blocks-in-xhtmlstring/
        private static IEnumerable<ContentFragment> GetStringReferences(XhtmlString xhtmlString)
        {
            if (xhtmlString?.Fragments?.Any() != true) return Enumerable.Empty<ContentFragment>();
            var contentLinks = new List<ContentFragment>();

            foreach (var fragment in xhtmlString.Fragments.GetFilteredFragments(PrincipalInfo.AnonymousPrincipal))
            {
                if (!(fragment is ContentFragment)) continue;
                var contentFragment = fragment as ContentFragment;
                if (ContentReference.IsNullOrEmpty(contentFragment.ContentLink)) continue;

                contentLinks.Add(contentFragment);
            }

            return contentLinks;

        }
    }
}