As we discussed in the previous section, the quality of a framework depends on its core features. The better the quality of the core, the better it will be for developing quality and maintainable applications. It's surprising to see the availability of a number of WordPress features directly related to web development, even though it is meant to create websites.

Let's get a brief introduction to the WordPress core features to see how they fit into web application development.

Built-in user management features are quite advanced in order to cater to the most common requirements of any web application. Its user roles and capability handling make it much easier to control the access to specific areas of your application. We can separate users into multiple levels using roles and then use capabilities to define the permitted functionality for each user level. Most full stack frameworks don't have built-in user management features, and hence this can be considered as an advantage of using WordPress.

File uploading and managing is a common and time consuming task in web applications. Media uploader, which comes built-in with WordPress, can be effectively used to automate the file-related tasks without writing much source code. A super-simple interface makes it so easy for application users to handle file-related tasks.

WordPress offers a simple template management system for its themes. It is not as complex or fully featured as a typical template engine. However, it offers a wide range of capabilities from a CMS development perspective, which we can extend to suit web applications.

In most scenarios, we will be using the existing database table structure for our application development. WordPress database management functionalities offer a quick and easy way of working with existing tables with its own style of functions. Unlike other frameworks, WordPress provides a built-in database structure, and hence most of the functionalities can be used to directly work with these tables without writing custom SQL queries.

Comprehensive support for routing is provided through permalinks. WordPress makes it simple to change the default routing and choose your own routing, in order to build search engine-friendly URLs.

Building an API is essential for allowing third-party access to our application. WordPress provides a built-in API for accessing CMS-related functionality through its XML-RPC interface. Also, developers are allowed to create custom API functions through plugins, making it highly flexible for complex applications.

The REST API makes it possible to give third-party access to the application data, similar to XML-RPC API. This API uses easy to understand HTTP requests and JSON format, making it easier to communicate with WordPress applications. JavaScript is becoming the modern trend in developing applications. So, the availability of JSON in the REST API will allow external users to access and manipulate WordPress data within their JavaScript-based applications.

Caching in WordPress can be categorized into two sections called persistent and nonpersistent caching. Nonpersistent caching is provided by the WordPress cache object while persistent caching is provided through its Transient API. Caching techniques in WordPress are simple compared to other frameworks, but it's powerful enough to cater for complex web applications.

As developers, you might have worked with cron jobs for executing certain tasks at specified intervals. WordPress offers the same scheduling functionality through built-in functions, similar to a cron job. However, WordPress cron execution is slightly different from normal cron jobs. In WordPress, cron won't be executed unless someone visits the site. Typically, it's used for scheduling future posts. However, it can be extended to cater complex scheduling functionality.

The power of WordPress comes from its plugin mechanism, which allows us to dynamically add or remove functionality without interrupting other parts of the application. Widgets can be considered as a part of the plugin architecture and will be discussed in detail further in this chapter.

The design of a WordPress site comes through the theme. This site offers many built-in template files to cater to the default functionality. Themes can be easily extended for custom functionality. Also, the design of the site can be changed instantly by switching to a compatible theme.

Actions and filters are part of the WordPress hook system. Actions are events that occur during a request. We can use WordPress actions to execute certain functionalities after a specific event is completed. On the other hand, filters are functions that are used to filter, modify, and return data. Flexibility is one of the key reasons for the higher popularity of WordPress compared to other CMSs. WordPress has its own way of extending functionality of custom features as well as core features through actions and filters. These actions and filters allow developers to build advanced applications and plugins, which can be easily extended with minor code changes. As a WordPress developer, it's a must to know the perfect use of these actions and filters in order to build highly-flexible systems.

WordPress offers a fully-featured backend for administrators as well as normal users. These interfaces can be easily customized to adapt to custom applications. All the application-related lists, settings, and data can be handled through the admin section.

The overall collection of features provided by WordPress can be effectively used to match the core functionalities provided by full stack PHP frameworks.