Great learning resource of that programming language anyway. For sure it's safe by any angle cause it's official one of all your cases. You do not need anything else in the world of PHP language except this resource honestly.
php.net is the official website for the php programming language. The documentation is a very good resource for both programmers starting out or even advanced programmers brushing up. Often the comments are filled with examples.
Server-side HTML embedded scripting language. It provides web developers with a full suite of tools for building dynamic websites: native APIs to Apache and other web servers; easy access to MySQL, Sybase, Oracle, and other databases; IMAP; LDAP; HTTP headers and cookies.