php-doc-en/language/oop5/paamayim-nekudotayim.xml

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 <sect1 xml:id="language.oop5.paamayim-nekudotayim" xmlns="http://docbook.org/ns/docbook">
  <title>Scope Resolution Operator (::)</title>

  <para>
   The Scope Resolution Operator (also called Paamayim Nekudotayim) or in
   simpler terms, the double colon, is a token that allows access to 
   <link linkend="language.oop5.static">static</link>,
   <link linkend="language.oop5.constants">constant</link>, and overridden 
   properties or methods of a class. 
  </para>

  <para>
   When referencing these items from outside the class definition, use
   the name of the class.
  </para>

  <para>
   As of PHP 5.3.0, it's possible to reference the class using a variable.
   The variable's value can not be a keyword (e.g. <literal>self</literal>,
   <literal>parent</literal> and <literal>static</literal>).
  </para>

  <para>
   Paamayim Nekudotayim would, at first, seem like a strange choice for
   naming a double-colon. However, while writing the Zend Engine 0.5
   (which powers PHP 3), that's what the Zend team decided to call it.
   It actually does mean double-colon - in Hebrew!
  </para>

  <example>
   <title>:: from outside the class definition</title>
   <programlisting role="php">
<![CDATA[
<?php
class MyClass {
    const CONST_VALUE = 'A constant value';
}

$classname = 'MyClass';
echo $classname::CONST_VALUE; // As of PHP 5.3.0

echo MyClass::CONST_VALUE;
?>
]]>
   </programlisting>
  </example>

  <para>
   Two special keywords <varname>self</varname> and <varname>parent</varname>
   are used to access properties or methods from inside the class definition.
  </para>

  <example>
   <title>:: from inside the class definition</title>
   <programlisting role="php">
<![CDATA[
<?php
class OtherClass extends MyClass
{
    public static $my_static = 'static var';

    public static function doubleColon() {
        echo parent::CONST_VALUE . "\n";
        echo self::$my_static . "\n";
    }
}

$classname = 'OtherClass';
echo $classname::doubleColon(); // As of PHP 5.3.0

OtherClass::doubleColon();
?>
]]>
   </programlisting>
  </example>

  <para>
   When an extending class overrides the parents definition of a method,
   PHP will not call the parent's method. It's up to the extended class
   on whether or not the parent's method is called. This also applies to <link
   linkend="language.oop5.decon">Constructors and Destructors</link>, <link
   linkend="language.oop5.overloading">Overloading</link>, and <link
   linkend="language.oop5.magic">Magic</link> method definitions.
  </para>

  <example>
   <title>Calling a parent's method</title>
   <programlisting role="php">
<![CDATA[
<?php
class MyClass
{
    protected function myFunc() {
        echo "MyClass::myFunc()\n";
    }
}

class OtherClass extends MyClass
{
    // Override parent's definition
    public function myFunc()
    {
        // But still call the parent function
        parent::myFunc();
        echo "OtherClass::myFunc()\n";
    }
}

$class = new OtherClass();
$class->myFunc();
?>
]]>
   </programlisting>
  </example>

 </sect1>
 
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