'hold my beer' with Sitecore

Sitecore 9.1 release has brought many useful features including Cortex - widely advertised integration and support for AI and ML. For now it covers 2 features: component personalisation suggestions and content tagging. The latter comes with an OOTB integration with OpenCalais API. This service provided by Thomson Reuters provides categorisation suggestions based on the meaning of provided content. Combined with Sitecore, it automatically assigns tags based on item's text fields content.

Unfortunately, it's fairly simple and does not cover tagging based on the image content. However, with the help of Microsoft Cognitive Services (Tag Image endpoint to be precise) we can make it work and get a collection of relevant tags.

Let's get to work. To start we need to figure out OOTB tagging architecture and how it works, so a quick look at Sitecore docs gives us a brief idea of what we need. What we'll do is extending the current content tagging pipeline, so that processing a media item will not only use OpenCalais (which must be active) with item's text fields to produce the tags, but also use the MS Cognitive Services to analyze the image and describe it with appropriate tags.

Precisely, what we need are 2 new providers:

• Content provider extracting the string of relevant information out of the item for further analysis
• Discovery provider containing the business logic behind processing extracted data and producing tags

Ideally, there should be also an initial validation processor encapsulating all the checks and aborting the pipeline in case of any issues (missing configuration etc.) or if the item is not a good fit for our custom tagging. In our case it's just a functional extension, so performing such an abortion would stop the whole Content Tagging pipeline, not just our additional functionality resulting in no tags assigned at all. Because of that and to simplify the code, I decided to move those checks to Content and Discovery providers. What's more, not all 4 of providers available to be put in the pipeline have to be implemented. That means that Content and Discovery ones will add extra image tags returned by the API for a further, standard processing performed by the latter 2 providers. The configuration of such extension looks as follows:

<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/" xmlns:role="http://www.sitecore.net/xmlconfig/role/">
  <sitecore>
    <contentTagging>
      <configurations>
        <config name="Default">
          <content>
            <provider name="ComputerVisionContentProvider"/>
          </content>
          <discovery>
            <provider name="ComputerVisionDiscoveryProvider"/>
          </discovery>
        </config>
      </configurations>
      <providers>
        <content>
          <add name="ComputerVisionContentProvider" type="Sitecore91.Foundation.Tagging.Providers.ComputerVisionContentProvider, Sitecore91.Foundation.Tagging" />
        </content>
        <discovery>
          <add name="ComputerVisionDiscoveryProvider" type="Sitecore91.Foundation.Tagging.Providers.ComputerVisionDiscoveryProvider, Sitecore91.Foundation.Tagging" />
        </discovery>
      </providers>
    </contentTagging>
  </sitecore>
</configuration>

Now, here's the Content provider extracting the taggable data from the item. Standard process is extraction of the item text fields and sending them down the pipeline for conversion into tags. In our case to tightly follow that purpose we'd have to serialize the image into byte array. Let's go for a different approach, extract just the image ID and pass it further so that we'll delegate and encapsulate this task within Discovery provider. The only check we make is if it's a media item which does not eliminate, but strongly reduce the number of unsupported items left for further processing.

using Sitecore.ContentTagging.Core.Models;
using Sitecore.ContentTagging.Core.Providers;
using Sitecore.Data.Items;

namespace Sitecore91.Foundation.Tagging.Providers
{
    public class ComputerVisionContentProvider : IContentProvider<Item>
    {
        public TaggableContent GetContent(Item item)
        {
            var stringContent = new StringContent();
            if (item.Paths.IsMediaItem)
            {
                stringContent.Content = item.ID.ToString();
            }
            return stringContent;
        }
    }
}

To align the business logic with the approach taken in Content provider, we need think on how to handle the 'special' case of processing the image item. Just to remind: the providers described here are just extending the existing pipeline, so we focus on handling this case only exclusively by processing the taggable content only if:

• all it contains is an item ID (it's been processed by our custom Content provider)
• the item is a media item (in this use case we're tagging images from media library only)
• the media item is an image (as only images will get correctly tagged by the service)

After that we just serialize such image and pass it to the service. Please keep in mind that we also have the other 'Tag' implementation accepting image URL which would make the API calls much faster. I just used the other overload as found it easier to use in development environment.

I also made use of the 'confidence' parameter to filter out the tags with less than 50% of confidence to filter out the potentially irrelevant tags.

using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using Microsoft.Extensions.DependencyInjection;
using Sitecore.ContentTagging.Core.Models;
using Sitecore.ContentTagging.Core.Providers;
using Sitecore.Data;
using Sitecore.Data.Items;
using Sitecore.DependencyInjection;
using Sitecore91.Foundation.CognitiveServices.ComputerVision;

namespace Sitecore91.Foundation.Tagging.Providers
{
    public class ComputerVisionDiscoveryProvider : IDiscoveryProvider
    {
        public IEnumerable<TagData> GetTags(IEnumerable<TaggableContent> content)
        {
            var computerVisionService = ServiceLocator.ServiceProvider.GetService<IComputerVisionService>();

            var tagDataList = new List<TagData>();
            foreach (StringContent stringContent in content)
            {
                if (string.IsNullOrEmpty(stringContent?.Content) || !ID.TryParse(stringContent.Content, out var itemId))
                    continue;

                var item = Sitecore.Configuration.Factory.GetDatabase("master").GetItem(itemId);
                if (!item.Paths.IsMediaItem)
                    continue;

                var mediaItem = new MediaItem(item);
                if (!mediaItem.MimeType.StartsWith("image/"))
                    continue;

                var image = (byte[]) new ImageConverter().ConvertTo(Image.FromStream(mediaItem.GetMediaStream()), typeof(byte[]));
                var result = computerVisionService.Analyze(image, "tags", "", "en");
                var tags = result.tags.Where(x => x.confidence > 0.5).Select(x => x.name);

                tagDataList.AddRange(tags.Select(tag => new TagData {TagName = tag}));
            }
            return tagDataList;
        }

        public bool IsConfigured()
        {
            return true;
        }
    }
}

From implementation point of view that's it - 2 providers extending the pipeline. All you have to do now to test the solution is to select a media item in Content Editor, select the Home tab in the ribbon and click Tag Item in Content Tagging section. After several seconds of processing of our sample image:

You can refresh the 'Tagging' section to see the following tags:

That aligns with the collection generated in my previous post where we directly hit the service with this exact image. We have 1 tag missing comparing with the previous tag set and that's the result of filtering using the 'confidence' field.

In my previous post we utilised MS Cognitive Services to assist with cropping images smart way on the fly. The reason for that was to reuse a single HQ image in different display size scenarios (pages / devices) focused on image's centre of interest rather than creating and maintaining a manually cropped collection.

Now, as we have the service implementation in place let's integrate it with SXA. Considering the purpose described above, a really good usage example is creating a new Rendering Variant field to process the referenced image according to provided size and cropping mode.

1. To start, create a Rendering Variant field template and tailor it for service's purpose by adding the minimal set of values needed to utilise the previously developed service:

2. Then, add this newly defined field to one of the Rendering Variants containing an image to crop:

Now some code backing up the functionality of created items:

3. In general, what we need to do is extending parseVariantFields and renderVariantField pipelines:

<?xml version="1.0" encoding="utf-8" ?>
<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
  <sitecore>
    <pipelines>
      <parseVariantFields>
        <processor type="Sitecore91.Foundation.SXAExtensions.Pipelines.VariantFields.SmartThumbnail.ParseSmartThumbnail, Sitecore91.Foundation.SXAExtensions" resolve="true"/>
      </parseVariantFields>
      <renderVariantField>
        <processor type="Sitecore91.Foundation.SXAExtensions.Pipelines.VariantFields.SmartThumbnail.RenderSmartThumbnail, Sitecore91.Foundation.SXAExtensions" resolve="true"/>
      </renderVariantField>
    </pipelines>
  </sitecore>
</configuration>

4. Then implement a new Rendering Variant field to be processed by those pipelines:

using Sitecore.Data.Items;
using Sitecore.XA.Foundation.RenderingVariants.Fields;

namespace Sitecore91.Foundation.SXAExtensions.Pipelines.VariantFields.SmartThumbnail
{
    public class SmartThumbnailVariant : RenderingVariantFieldBase
    {
        public int Width { get; set; }
        public int Height { get; set; }
        public bool IsSmartCrop { get; set; }

        public SmartThumbnailVariant(Item variantItem) : base(variantItem) { }
    }
}

5. Followed by the processor responsible for parsing the Rendering Variant field:

using Sitecore.Data;
using Sitecore.XA.Foundation.Variants.Abstractions.Pipelines.ParseVariantFields;

namespace Sitecore91.Foundation.SXAExtensions.Pipelines.VariantFields.SmartThumbnail
{
    public class ParseSmartThumbnail : ParseVariantFieldProcessor
    {
        public override ID SupportedTemplateId => Constants.RenderingVariants.SmartThumbnail.Fields.SmartThumbnailVariant;

        public override void TranslateField(ParseVariantFieldArgs args)
        {
            var variantFieldsArgs = args;

            var smartThumbnail = new SmartThumbnailVariant(args.VariantItem)
            {
                ItemName = args.VariantItem.Name,
                FieldName = args.VariantItem.Fields[Constants.RenderingVariants.SmartThumbnail.Fields.FieldName].GetValue(true),
                Width = int.TryParse(args.VariantItem.Fields[Constants.RenderingVariants.SmartThumbnail.Fields.Width].GetValue(true), out var width) ? width : 0,
                Height = int.TryParse(args.VariantItem.Fields[Constants.RenderingVariants.SmartThumbnail.Fields.Height].GetValue(true), out var height) ? height : 0,
                IsSmartCrop = int.TryParse(args.VariantItem.Fields[Constants.RenderingVariants.SmartThumbnail.Fields.IsSmartCrop].GetValue(true), out var smartCropValue) && smartCropValue == 1
            };
            variantFieldsArgs.TranslatedField = smartThumbnail;
        }
    }
}

Where Constants is a standard helper class with static IDs:

using Sitecore.Data;

namespace Sitecore91.Foundation.SXAExtensions
{
    public struct Constants
    {
        public struct RenderingVariants
        {
            public struct SmartThumbnail
            {
                public struct Fields
                {
                    public static ID SmartThumbnailVariant => new ID("{00458333-70A1-4D52-B375-62CBE13575CD}");
                    public static ID FieldName => new ID("{0B00BC72-0C1C-4A49-8C94-297E38E511E7}");
                    public static ID Width => new ID("{51A093C8-A516-4A70-8223-7B907DCB0958}");
                    public static ID Height => new ID("{6447EF7A-D84E-4CA9-9F57-7A7AC6FE87D6}");
                    public static ID IsSmartCrop => new ID("{4C4899C4-CA85-451A-9FEE-ECCD678D01FD}");
                }
            }
        }
    }
}

6. Finally, Rendering Variant field where the actual service call and rendering HTML preparation take place:

using System;
using System.Drawing;
using System.IO;
using System.Web.UI.HtmlControls;
using Sitecore.Data.Fields;
using Sitecore.Data.Items;
using Sitecore.Resources.Media;
using Sitecore.SecurityModel;
using Sitecore.XA.Foundation.RenderingVariants.Pipelines.RenderVariantField;
using Sitecore.XA.Foundation.Variants.Abstractions.Models;
using Sitecore.XA.Foundation.Variants.Abstractions.Pipelines.RenderVariantField;
using Sitecore91.Foundation.CognitiveServices.ComputerVision;

namespace Sitecore91.Foundation.SXAExtensions.Pipelines.VariantFields.SmartThumbnail
{
    public class RenderSmartThumbnail : RenderRenderingVariantFieldProcessor
    {
        private readonly IComputerVisionService _computerVisionService;
        public override Type SupportedType => typeof(SmartThumbnailVariant);
        public override RendererMode RendererMode => RendererMode.Html;

        public RenderSmartThumbnail()
        {
            _computerVisionService = ServiceLocator.ServiceProvider.GetService<IComputerVisionService>();
        }

        public override void RenderField(RenderVariantFieldArgs args)
        {
            var variantField = args.VariantField as SmartThumbnailVariant;
            var imageUrl = default(string);

            if (args.Item != null && !string.IsNullOrWhiteSpace(variantField?.FieldName))
            {
                ImageField imageField = args.Item.Fields[variantField.FieldName];
                if (imageField?.MediaItem != null)
                {
                    var thumbNameSuffix = "_thumb";
                    var newItemPath = imageField.MediaItem.Paths.Path + thumbNameSuffix;
                    var mediaItem = (MediaItem) imageField.MediaItem;

                    var thumbMediaItem = mediaItem.Database.GetItem(newItemPath);
                    if (thumbMediaItem != null)
                    {
                        using (new SecurityDisabler())
                        {
                            thumbMediaItem.Delete();
                        }
                    }

                    var image = (byte[])new ImageConverter().ConvertTo(Image.FromStream(mediaItem.GetMediaStream()), typeof(byte[]));
                    var thumbnail = _computerVisionService.GetThumbnail(image, variantField.Width, variantField.Height, variantField.IsSmartCrop);

                    if (thumbnail == null)
                    {
                        return;
                    }

                    using (var memoryStream = new MemoryStream(thumbnail))
                    {
                        var mediaCreator = new MediaCreator();
                        var options = new MediaCreatorOptions
                        {
                            Versioned = false,
                            IncludeExtensionInItemName = false,
                            Database = mediaItem.Database,
                            Destination = newItemPath,
                            FileBased = false
                        };

                        using (new SecurityDisabler())
                        {
                            var newFileName = mediaItem.Name + thumbNameSuffix + "." + mediaItem.Extension;
                            thumbMediaItem = mediaCreator.CreateFromStream(memoryStream, newFileName, options);
                        }
                    }
                    imageUrl = MediaManager.GetMediaUrl(thumbMediaItem);
                }
            }

            if (string.IsNullOrWhiteSpace(imageUrl))
            {
                return;
            }

            var control = new HtmlGenericControl("img");
            control.Attributes.Add("src", imageUrl);

            args.ResultControl = control;
            args.Result = RenderControl(args.ResultControl);
        }
    }
}

If all gone well, we should see a smartly (considering the image centre of interest) cropped to desired size image as a part of our Rendering Variant:

The given example is just an outline use case that generates some simple HTML code to display the image. Naturally, it can be extended further to offer more flexibility, e.g. like the 'Responsive Image' field does.

One of the field types for display with Rendering Variants is Template. It allows you to define your own NVelocity template to embed custom processing of the output. The really cool thing about it that it can be made flexible even further and extended by adding custom renderers.

The templates mentioned above are processed by getVelocityTemplateRenderers SXA pipeline outlined here. That gives us a trace that this could be achieved with extending the pipeline by adding a custom AddTemplateRenderers processor. Taking a closer look with ILSpy at Sitecore.XA.Foundation.Variants.Abstractions.dll reveals that we can do that by implementing the IGetTemplateRenderersPipelineProcessor.

SXA docs for Creating a Rendering Variant available here describe a predefined set of objects and tools provided with SXA to use in the template:

• $item: access to the current item ($item.Name displays current item name).
• $dateTool.Format(date, format): formats date and time values.
• $numberTool.Format(number, format): formats numbers.
• $geospatial: in case of geospatial search ($geospatial.Distance) will show distance to certain point of interest).

What's really cool, you can easily extend this list and implement a custom renderer with business logic of your choice. Some good usage examples could be your company's real-time share price or current weather in your location. However, as Sitecore community is well known for it's outstanding sense of humour we need to keep up - let's create a tool rendering a random joke for display.

First, to locate where to hook our implementation, let's have a look into the getVelocityTemplateRenderers pipeline:

<getVelocityTemplateRenderers patch:source="Sitecore.XA.Foundation.Variants.Abstractions.config">
  <processor type="Sitecore.XA.Foundation.Variants.Abstractions.Pipelines.GetVelocityTemplateRenderers.InitializeVelocityContext, Sitecore.XA.Foundation.Variants.Abstractions" resolve="true"/>
  <processor type="Sitecore.XA.Foundation.Variants.Abstractions.Pipelines.GetVelocityTemplateRenderers.AddTemplateRenderers, Sitecore.XA.Foundation.Variants.Abstractions" resolve="true"/>
</getVelocityTemplateRenderers>

Based on the decompiled implementation of AddTemplateRenderers processor, we just need to inject another entry into the pipeline context. This should do the trick:

using Sitecore.XA.Foundation.Variants.Abstractions.Pipelines.GetVelocityTemplateRenderers;

namespace Sitecore91.Foundation.SXAExtensions.Pipelines.NVelocityTemplateRenderers
{
    public class AddCustomTemplateRenderers : IGetTemplateRenderersPipelineProcessor
    {
        public void Process(GetTemplateRenderersPipelineArgs args)
        {
            args.Context.Put("jokeTool", new JokeTool());
        }
    }
}

Our implementation of JokeTool consumes the Geek Jokes API to provide us with a random joke on each pipeline execution (at least as long as it's not cached):

using System;
using System.Net.Http;

namespace Sitecore91.Foundation.SXAExtensions.Pipelines.NVelocityTemplateRenderers
{
    public class JokeTool
    {
        public string GetRandomJoke()
        {
            var jokeApiUrl = "https://geek-jokes.sameerkumar.website/api";
            try
            {
                using (var httpClient = new HttpClient())
                {
                    return httpClient.GetStringAsync(jokeApiUrl).GetAwaiter().GetResult();
                }
            }
            catch (Exception e)
            {
                return "No jokes today.";
            }
        }
    }
}

Having code in place, let's wire it up with an appropriate patch in the end of pipeline:

<?xml version="1.0" encoding="utf-8" ?>
<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
  <sitecore>
    <pipelines>
      <getVelocityTemplateRenderers>
        <processor type="Sitecore91.Foundation.SXAExtensions.Pipelines.NVelocityTemplateRenderers.AddCustomTemplateRenderers, Sitecore91.Foundation.SXAExtensions" 
                   patch:after="processor[@type='Sitecore.XA.Foundation.Variants.Abstractions.Pipelines.GetVelocityTemplateRenderers.AddTemplateRenderers, Sitecore.XA.Foundation.Variants.Abstractions']" />
      </getVelocityTemplateRenderers>
    </pipelines>
  </sitecore>
</configuration>

What should result in amending the pipeline as below:

<getVelocityTemplateRenderers patch:source="Sitecore.XA.Foundation.Variants.Abstractions.config">
  <processor type="Sitecore.XA.Foundation.Variants.Abstractions.Pipelines.GetVelocityTemplateRenderers.InitializeVelocityContext, Sitecore.XA.Foundation.Variants.Abstractions" resolve="true"/>
  <processor type="Sitecore.XA.Foundation.Variants.Abstractions.Pipelines.GetVelocityTemplateRenderers.AddTemplateRenderers, Sitecore.XA.Foundation.Variants.Abstractions" resolve="true"/>
  <processor type="Sitecore91.Foundation.SXAExtensions.Pipelines.NVelocityTemplateRenderers.AddCustomTemplateRenderers, Sitecore91.Foundation.SXAExtensions" patch:source="AddCustomTemplateRenderers.config"/>
</getVelocityTemplateRenderers>

To see in action our newly created tool, we use it with the Template field just like the other already predefined ones (e.g. $dateTool):

Now you can enjoy your day with a fresh portion of wisdom on each page visit:

That was literally fun.

Rendering Variants offer convenient way of customising how SXA components get rendered. One of the most frequently used fields for building rendering variants is Query, which allows you to utilise item(s) out of the component's scope.

What SXA offers out of the box is a decent collection of predefined, routinely used tokens which help to simplify the queries and makes their usage much more convenient. They are listed here in the SXA docs for resolveTokens pipeline:

• $compatibleThemes - path to all themes
• $theme - currently used theme
• $pageDesigns - root of page designs
• $partialDesigns - root of partial designs
• $currenttemplate - name of the current template
• $tenant - path to the current tenant
• $site - path to the current site
• $home - path to the current site start item (Home)
• $templates - path to the current site templates
• $siteMedia - path to Virtual Media folder located under site

As you can see, it contains the most handy tokens we might need for building queries, such as home item ($home) or component template ($currentTemplate). Of course every application, depending on its business specific needs, 'develops' along the time it's own crucial nodes which become frequently referenced and used in the queries. Very good example is the root item for articles, which occurs in every web site offering news to the user.

In the following use case we will create $articles token referring to articles, which will be translated by resolveTokens pipeline as a query returning all items implementing template Article under the Articles root node.

Technically, what we need to do is extending the resolveTokens pipeline:

<resolveTokens patch:source="Sitecore.XA.Foundation.Multisite.config">
  <processor type="Sitecore.XA.Foundation.Multisite.Pipelines.ResolveTokens.ResolveMultisiteTokens, Sitecore.XA.Foundation.Multisite" resolve="true"/>
  <processor type="Sitecore.XA.Foundation.Presentation.Pipelines.ResolveTokens.ResolvePresentationTokens, Sitecore.XA.Foundation.Presentation" resolve="true" patch:source="Sitecore.XA.Foundation.Presentation.config"/>
  <processor type="Sitecore.XA.Foundation.Theming.Pipelines.ResolveTokens.ResolveThemingTokens, Sitecore.XA.Foundation.Theming" resolve="true" patch:source="Sitecore.XA.Foundation.Theming.config"/>
  <processor type="Sitecore.XA.Foundation.TokenResolution.Pipelines.ResolveTokens.CurrentTemplateToken, Sitecore.XA.Foundation.TokenResolution" resolve="true" patch:source="Sitecore.XA.Foundation.TokenResolution.config"/>
  <processor type="Sitecore.XA.Foundation.TokenResolution.Pipelines.ResolveTokens.EscapeQueryTokens, Sitecore.XA.Foundation.TokenResolution" resolve="true" patch:source="Sitecore.XA.Foundation.TokenResolution.config"/>
</resolveTokens>

by adding a new processor handling the custom token.

To figure out what exactly has to be implemented and how are the currently existing processors handling the predefined tokens, we can use ILSpy, dotPeek or any other .NET decompiler to take a closer look at Sitecore.XA.Foundation.TokenResolution.dll. It turns out that to extend the resolveTokens pipeline to handle custom token resolution, we need to implement the Pipelines.ResolveTokens.ResolveTokensProcessor abstract class.

To fulfill the use case mentioned before, I implemented it this way:

using Sitecore.Data.Items;
using Sitecore.XA.Foundation.TokenResolution.Pipelines.ResolveTokens;

namespace Sitecore91.Foundation.SXAExtensions.Pipelines.Tokens
{
    public class ResolveCustomTokens : ResolveTokensProcessor
    {
        public override void Process(ResolveTokensArgs args)
        {
            args.Query = ReplaceTokenWithValue(args.Query, "$articles", () => GetArticles(args.ContextItem));
        }

        private string GetArticles(Item contextItem)
        {
            var articlesRootPath = contextItem.Database.GetItem(Constants.Items.ArticlesHome).Paths.FullPath;
            var templateId = Constants.Templates.Article.ToString();

            return articlesRootPath + "//*[@@templateid='" + templateId + "']";
        }
    }
}

Just to clarify, Constants static class used in the processor is just a standard helper containing IDs of frequently used items:

using Sitecore.Data;

namespace Sitecore91.Foundation.SXAExtensions
{
    public struct Constants
    {
        public struct Items
        {
            public static ID ArticlesHome { get { return new ID("{4109F746-326F-4EF9-9BEB-D14261E8BD83}"); } }
        }

        public struct Templates
        {
            public static ID Article { get { return new ID("{3A98D12C-1911-49A6-8F8E-AAEDBCC9C3FD}"); } }
        }
    }
}

As the implementation code is in place we're almost there, what’s left is just wiring it up in the pipeline. We locate the processor right before the last one in the resolveTokens pipeline:

<?xml version="1.0" encoding="utf-8" ?>
<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
  <sitecore>
    <pipelines>
      <resolveTokens>
        <processor type="Sitecore91.Foundation.SXAExtensions.Pipelines.Tokens.ResolveCustomTokens, Sitecore91.Foundation.SXAExtensions" 
                   patch:before="processor[@type='Sitecore.XA.Foundation.TokenResolution.Pipelines.ResolveTokens.EscapeQueryTokens, Sitecore.XA.Foundation.TokenResolution']" />
      </resolveTokens>
    </pipelines>
  </sitecore>
</configuration>

To double check the result, pipeline after the amendments should look like this:

<resolveTokens patch:source="Sitecore.XA.Foundation.Multisite.config">
  <processor type="Sitecore.XA.Foundation.Multisite.Pipelines.ResolveTokens.ResolveMultisiteTokens, Sitecore.XA.Foundation.Multisite" resolve="true"/>
  <processor type="Sitecore.XA.Foundation.Presentation.Pipelines.ResolveTokens.ResolvePresentationTokens, Sitecore.XA.Foundation.Presentation" resolve="true" patch:source="Sitecore.XA.Foundation.Presentation.config"/>
  <processor type="Sitecore.XA.Foundation.Theming.Pipelines.ResolveTokens.ResolveThemingTokens, Sitecore.XA.Foundation.Theming" resolve="true" patch:source="Sitecore.XA.Foundation.Theming.config"/>
  <processor type="Sitecore.XA.Foundation.TokenResolution.Pipelines.ResolveTokens.CurrentTemplateToken, Sitecore.XA.Foundation.TokenResolution" resolve="true" patch:source="Sitecore.XA.Foundation.TokenResolution.config"/>
  <processor type="Sitecore91.Foundation.SXAExtensions.Pipelines.Tokens.ResolveCustomTokens, Sitecore91.Foundation.SXAExtensions" patch:source="ResolveCustomTokens.config"/>
  <processor type="Sitecore.XA.Foundation.TokenResolution.Pipelines.ResolveTokens.EscapeQueryTokens, Sitecore.XA.Foundation.TokenResolution" resolve="true" patch:source="Sitecore.XA.Foundation.TokenResolution.config"/>
</resolveTokens>

OK, backend to support the $articles token is done, so let's start making use of it.

In Content Editor I created the Landing Page rendering variant to display few page values: Title, Published date and a Query referring to the collection of articles:

Of course, as articles are usually quite complex items, let's tailor their display to absolute minimum showing only their names for this example purpose. To achieve that, I added a child field of type Template to the Articles query and called it Name.

Template field thanks to the support of NVelocity templates refers to its context (article) item by usage of $item token. This means that for each returned article we select and display only it's name:

That's it.

Now, after making sure I applied the Landing Page rendering variant to the desired component, I am presented with the fields corresponding to the content of the item: Title, Published date, together with all (4, it's a test) of the articles names:

Hope this helps.