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HTML / CSS / JS

<?php
$errors = [];
$values = [];

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    // Required field
    $name = trim($_POST['name'] ?? '');
    if ($name === '') {
        $errors['name'] = 'Name is required.';
    } elseif (strlen($name) < 2) {
        $errors['name'] = 'Name must be at least 2 characters.';
    } else {
        $values['name'] = $name;
    }

// Email validation
    $email = trim($_POST['email'] ?? '');
    if ($email === '') {
        $errors['email'] = 'Email is required.';
    } elseif (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
        $errors['email'] = 'Please enter a valid email address.';
    } else {
        $values['email'] = $email;
    }

// Numeric range
    $age = $_POST['age'] ?? '';
    if (!is_numeric($age) || $age < 18 || $age > 120) {
        $errors['age'] = 'Age must be a number between 18 and 120.';
    } else {
        $values['age'] = (int) $age;
    }

if (empty($errors)) {
        // All valid — process the form
        echo 'Form submitted successfully!';
    }
}