GUIDES
The three visibility keywords control where a property or method can actually be accessed from — the distinction between protected and private specifically comes down to whether a subclass gets access too.
PHP classes can only extend one parent — traits are the language's answer to needing the same reusable method in several otherwise-unrelated classes without that single-inheritance limit getting in the way.
Composer manages a project's external library dependencies and their versions — every modern PHP framework, Laravel included, is built on top of it, not alongside it.
Three separate php.ini directives all cap upload size independently — raising just one and leaving the others at their default is the most common reason this fix doesn't seem to work.
PDO is the modern, framework-agnostic way to talk to MySQL from plain PHP — and prepared statements aren't optional if user input touches the query.
public, protected, and private control which code is allowed to touch a class's properties and methods — the same three-level model works nearly identically across PHP, Java, and most other OOP languages.
$_REQUEST reads from GET, POST, and cookies all at once — which sounds convenient until two of those sources happen to define the same key, and precedence quietly decides which value wins.
A prepared statement isn't an optional refinement over string-concatenated SQL — it's the actual fix for SQL injection, which string escaping alone doesn't fully close off.
The $_FILES superglobal and move_uploaded_file() are what Laravel's own file upload handling is built on top of — worth understanding directly, even in a framework-based project.
Composer resolves dependencies per-project, not globally — this is exactly why two Laravel projects on the same machine can run entirely different, mutually incompatible versions of the same package without conflict.
A CLI php.ini and the web server's own php.ini are frequently two entirely different files — editing the one php -i reports rarely fixes an upload limit that only ever applies to requests through the web server.
A trait solves the exact problem PHP's single-inheritance model creates — reusing the same method implementation across classes that can't share a common parent class at all.
