Description:
------------
I need to restrict the direct setting of DOM* properties to ensure that no non-utf8 encoding is getting into the Document because libxml2 (ext/dom?) still can't handle that. Implementing this i discovered that classes derived from DOM* cannot restrict the access level of properties.
I think there should at least be an error raised telling that it is not allowed to change the access level of properties, but because of libxml's great  segfaulting abilities i would prefer to able to restrict the access (without a magic setter). Another solution for the encoding problem might be to just check _all_ incoming strings into the DomDocument for unicode if the documents encoding is UTF-8.

Reproduce code:
---------------
<?php
class Test extends DomDocument {
    protected $textContent;   
}

$test = new Test;
$test->loadXml('<foo>bar</foo>');
var_dump($test->textContent);

Expected result:
----------------
Fatal Error: Cannot access protected property Text::$textContent

Actual result:
--------------
string(3) "bar"