Basic data types: string, number, array and date and time.
Program building blocks: variables, functions, classes, and objects.
Web programming: cookies, forms, sessions and authentication.
Access databases using PDO, SQLite and other extensions.
RESTful API clients and servers, including HTTP, XML and OAuth.
Key concepts: email, regular expressions, and graph creation.
Designing robust applications: security and encryption, error handling, debugging and testing, and performance tuning.
Command line interface for files, directories and PHP.
Libraries and package managers such as Composer and PECL.