I found no duplicate.

PHP supports class constants:

    class A
    {
        const CONSTANT = 3;
    }

Can be refered to like this:

    echo A::CONSTANT;

And, just like static properties, class constants can be refered to through an instance of the class:

    $a = new A();
    echo $a::CONSTANT;

This works in Netbeans. But now, let's do the same using properties of an object, instead of simple variables:

    class B
    {
        private $a;

        public function f()
        {
            $this->a = new A();
            $foo = $this->a::CONSTANT; // doesn't work as expected, in PHP, but makes no error in netbeans
            $bar = ($this->a)::CONSTANT // works nicely but raises an error in Netbeans
        }
    }

Hope it's clear enough, but feel free to ask me for more details. I tested in the today's nightly (septembre 7th, 2016)