The default posts in WordPress only contain basic fields such as title, content, categories, and tags. These fields are primarily used for blogging purposes. In advanced application development, we use custom post types to manage various content types. So, we need advanced fields and advanced field types to manage additional data for each content type. In the previous recipe, we created a custom field type called the book. We need additional data such as book prices, pages, authors, and so on.
WordPress provides support for additional data capturing through built-in custom fields, as well as hooks for creating our own fields.

In this recipe, we are going to capture additional book data using built-in custom fields, as well as custom forms with custom fields.