Description:
------------
I've found cool feature that isn't documented yet so it is as undefined behavior. And works in all PHP since 5.0.2+ and/or earlier.
I.e. missing documentation for multiple declaration visibility and/or constants.

http://php.net/manual/en/language.oop5.visibility.php
http://php.net/manual/en/language.oop5.constants.php

Demo: https://3v4l.org/qRnlk

Test script:
---------------
<?php

class test1
{
    const a = 'b', b = 'a', c = 'c';

    public function __construct()
    {
        echo self::b, self::a, self::c, PHP_EOL;
    }
}

class test2
{
    private $a = 'b', $b = 'a', $c = 'c';
}

try {
    new test1; // abc
    echo test2::$b, test2::$a, test2::$c; // Cannot access private property test2::$b
} catch (Error $e) {
    echo $e->getMessage();
}