Behaviour of weak type check (string/float)

add.php

<?php
function add(float $a, float $b): float {
    return $a + $b;
}

main.php

<?php
require "add.php";

var_dump(add("1", "1"));
// float(2)

var_dump(add("1", "1foo"));
// PHP Notice:  A non well formed numeric value encountered
// float(2)

var_dump((float) "foo");
// float(0)

var_dump(floatval("foo"));
// float(0)

var_dump(add("1", "foo"));
// PHP Fatal error:  Uncaught TypeError: Argument 2 passed to add() must be of the type float, string given

The example was taken from https://wiki.php.net/rfc/scalar_type_hints_v5#example, modified and tested with PHP 7.1.12-3+ubuntu16.04.1+deb.sury.org+1 (cli).