HTML Form validation with PHP

I'm kinda new to PHP and I'm trying to make a script to validate a HTML form only with PHP (I know there are options to do so with JS, but I guess it's better to have a "cover" with a server-side script).

Project folder structure:

project/
classes/ #contains classes to validate and process the HTML form
DB.php #contains the connection to the MySQL server
Rules.php #contains all rules to validate the form
Validate.php #contains methods to validate each field
Register.php #is the registration class
ini.php #contains the spl_autoload_register() function
index.php #contains the HTML form


HTML form code, which is located in the project folder:



register:
*









classes/ini.php

error_reporting(E_ALL);
ini_set('display_errors','On');

spl_autoload_register(function($class){
require_once $class.'.php';
});


classes/DB.php

`class DB
{
private $driver = 'mysql';
private $host = '127.0.0.1';
private $user = 'root';
private $pass = '';
private $name = 'project';
public $db;

public function __construct()
{
try
{
$this->db = new PDO("$this->driver:host=$this->host;dbname=$this->name;charset=utf8", $this->user, $this->pass);

//Error reporting. Throw exceptions
$this->db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

//Use native prepared statements
$this->db->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);

//Don't use persistent connections across multiple server sessions
$this->db->setAttribute(PDO::ATTR_PERSISTENT, false);

//Set default fetch mode
$this->db->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_OBJ);

//Return the connection object
return $this->db;
} catch (PDOException $e)
{
#echo 'Sorry. We have some problemes. Try again later!';

Use boolean expressions directly

Rules.php is full of ternaries that return true or false,
like this one:

public static function minlen($str, $value)
{
    return mb_strlen(trim($str)) < $value ? true : false;
}

You can return boolean expressions directly:

return mb_strlen(trim($str)) < $value;

Don't repeat yourself

All the rules trim the input.
Instead of writing trim in all of them,
it would be simpler to trim once before using the rule methods,
so that you don't have to repeatedly write trim so many times in every single method.

Don't return two types of values

The validateName may return two kinds of values:
an array of errors, or true (boolean).

if (isset($errors['name'])) {
        return $errors['name'];
    } else {
        return true;
    }

This is poor design.
Return one type of value.
If there are no errors, return an empty array.
That way the return type will be consistently an array,
which is a good thing.
The code snippet above will become simpler too:

return $errors['name'];

StackExchange Code Review Q#95879, answer score: 7