Description:
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From the documentation it is unclear:

What happens when I want to assign a property by reference using ReflectionProperty::setValue.
Also unclear what happens with ReflectionProperty::getValue.

Maybe this should also be a Feature Request, requesting additional methods that set a reference / return a reference.

In my opinion it is not necessary to create a special getValueByRef method, only the setValueByRef is necessary (getValue could always return by ref because you still need the other & for it to work).

Reproduce code:
---------------
class MyClass {
  public $myProperty;
}
$obj = new MyClass;
$globalProp = 'value1';
$refl = new ReflectionObject($obj);
$reflProp = $refl->getProperty('myProperty');
$reflProp->setValue($obj, $globalProp);

$globalProp = 'value2';

// what will the next line print: value1 or value2 => not clear from the documentation
echo $obj->myProperty; // prints value1
//------
class MyClass {
  public $myProperty = 'value1';
}
$obj = new MyClass;
$refl = new ReflectionObject($obj);
$reflProp = $refl->getProperty('myProperty');
$globalProp = & $reflProp->getValue($obj);

$globalProp = 'value2';

// what will the next line print: value1 or value2 => unclear according to docs
echo $obj->myProperty; // print value1 & E_STRICT is raised