What are best practices for organizing and including PHP documents within a project?

Best practices for organizing and including PHP documents within a project involve creating separate files for different functionalities, using a consistent naming convention, and organizing files into logical directories. Including PHP files can be done using the `include` or `require` statements, depending on whether the included file is essential for the script to run.

// Example of including a PHP file using require_once
require_once 'path/to/file.php';