Description:
------------
---
From manual page: https://php.net/closure.bind
---
Here is the description of the parameter newscope. 

newscope: The class scope to which associate the closure is to be associated, or 'static' to keep the current one. If an object is given, the type of the object will be used instead. This determines the visibility of protected and private methods of the bound object. It is not allowed to pass (an object of) an internal class as this parameter.

First, though English is not my first language, the first sentence seems to be bugged. Second, the third sentence might be misinterpreted as describing the main purpose of the parameter. It's not, because the closure does not even need to be bound. You even give an example of this fact in the example 

$bcl1 = Closure::bind($cl1, null, 'A');

Here is another interesting example:

$a = new A();
$bcl3 = Closure::bind(function () use($a) {return $a->ifoo;}, null, 'A'); 

The first sentence could simply say that the parameter is the class scope of the new closure, or "static" to keep the current one. The third sentence could be 

   "In particular, it affects whether the closure can access the protected 
    and private methods of the bound object, if any." 

The "In particular" makes clear that it is not the main thing that it does. The "if any" makes clear that the bound object is not required.