New coding standard: Code style for declare(strict_types=1);

Strict type decleration

If you define strict types for a PHP file, place the declare statement on a new line after the opening PHP tag surrounded by empty newlines. If the PHP file has a file level docblock the declare statement should be positioned after that. The declare statement is written without spaces around the equals sign.

<?php

/**
 * @file
 * This is a file docblock.
 */

declare(strict_types=1);

This is documented in the PHP Coding standards at Strict type declaration.