Plugins are the heart of WordPress, which makes web applications possible. WordPress plugins are used to extend its core features as independent modules. As a developer, it's important to understand the architecture of WordPress plugins and design patterns in order to be successful in developing large-scale applications.

Anyone who has basic programming knowledge can create plugins to meet application-specific requirements. However, it takes considerable effort to develop plugins that are reusable across a wide range of projects. In this chapter, we will build a few plugins to demonstrate the importance of reusability and extensibility. WordPress developers who don't have good experience in web application development shouldn't be skipping this chapter as plugins are the most important part of web application development.

I will assume that you have sound knowledge of basic plugin development using existing WordPress features in order to be comfortable...