 Hey, I'm Andrew Connell. This video is an overview of one of the chapters in my course, Mastering the SharePoint Framework that's available for purchase on my site, boytanos.io. This overview video is going to give you an idea of everything that the chapter covers. You can learn more by checking out the description and the notes below the video. If you got any questions about this chapter or about the course in general, just make sure you drop a comment below the video and I'll be sure to get back to you. So with that, let me get out of the way. Enjoy the overview to this chapter. Hello and welcome back to my course on Mastering the SharePoint Framework. Now this chapter is going to teach you how you can customize and extend the SharePoint user interface and experience using the SharePoint Framework. Extensions are one of those types of components that the SharePoint Framework supports in addition to web parts, library components, and adaptive card extensions. Now, as I said, the SharePoint Framework extensions are used to extend the SharePoint user interface in a way that differs from other types of components that I just talked about. For instance, you can use them to add a header or a footer across all pages in a site, inject JavaScript to all pages in a site, customize how a particular column is rendered in SharePoint lists, or customize list forms with the SharePoint Framework. Now, extensions were introduced in the SharePoint Framework very soon after the framework was released in 2017, and they're mostly available in all SharePoint deployments, except for SharePoint Server 2016, because they require the modern experience, and SharePoint Server 2016 only has the classic experience. Now, the initial motivation of extensions was to provide developers an option to implement similar customization options that we had in SharePoint before the SharePoint Framework existed, and we used to do those things with a classic experience. Now, the first and probably most common type of extension is an application customizer. The app customizer can be deployed to all pages in a site or across an entire tenant. Now, they allow you to run JavaScript on every page in a site or in the entire tenant, and you can also use it to add a content placeholder that's pinned either to the top of the page in the header or in the footer of the pages in the same scope as the script. So it's either in all pages in a site or all pages in all sites throughout the entire tenant. Now, you seasoned SharePoint developers, you may remember delegate controls and script link controls. The application customizer extension is the SharePoint Framework and modern page answer to those classic mode extensibility options. The list view command extension allows developers to add a button to the toolbar or in the context menu of an item within a SharePoint list or library. Your custom component can then do whatever you want it to do when someone clicks on that button. You seasoned SharePoint developers, now you may remember custom actions in the classic experience. That's what commands that are intended to replace in the modern experience with the SharePoint Framework. Now, developers can also use something called a field customizer, which is another type of a SharePoint Framework extension to define how a field, also known as a site column, should be rendered in a list grid view. Now, experienced SharePoint developers, you may remember this thing called JS Link or the client-side rendering framework, also known as CSR, back from that classic experience. Well, if you want to do those same customizations in a modern experience, you're going to use field customizers. And another type of SharePoint Framework extension is the list form customizer, also referred to as just form customizers. These were introduced in the 1.15 release of the SharePoint Framework, and these are going to allow developers to use the SharePoint Framework to define custom forms for SharePoint lists, including display forms, edit forms, and new forms. Form customizers are the developers' SPFX alternative to using power apps to implementing custom forms. Now, in this chapter, I'm going to walk through each of these different types of extensions, and in the next lesson, I'm going to start with some common topics around development, debugging, and the deployment for all these different extensions. So, let's get started, and I'll see you in the next lesson.