add scope resolution operator

concepts/scope-resolution-operator/.meta/config.json

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+{
+  "blurb": "The Scope Resolution Modifier (`::`)",
+  "authors": ["neenjaw"],
+  "contributors": []
+}

concepts/scope-resolution-operator/about.md

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+# Scope Resolution Operator
+
+The scope resolution operator (`::`) allows us to reference a class to access its name constants, static properties, or static methods.
+
+```php
+class MyClass
+{
+  public const MY_VALUE = 1;
+}
+
+// MyClass::class => "MyClass"
+// MyClass::MY_VALUE => 1
+```
+
+## Using `self` and `static` with the Scope Resolution Operator
+
+It may be required for an object to reference its own scope. To facilitate this, the `self` keyword allows a class to reference its own scope. Using the `self` keyword decouples the class from its own name -- making it easier to maintain code over time.
+
+```php
+class MyClass
+{
+  public const MY_VALUE = 1;
+
+  public function getMyValue(): int
+  {
+    return self::MY_VALUE;
+  }
+}
+
+// (new MyClass)->getMyValue() => 1
+```
+
+However, `self` is lexicographically bound to the class it appears in.
+
+```php
+class MyOtherClass extends MyClass
+{
+  public const MY_VALUE = 99;
+}
+
+// (new MyOtherClass)->getMyValue() => 1
+```
+
+Evaluating `MyOtherClass::getMyValue` still results in `1` rather than `99`. To work around this, use the `static` keyword with the scope resolution operator to "late bind" the reference to the current descendent class.
+
+```php
+// Update MyClass:
+class MyClass
+{
+  public const MY_VALUE = 1;
+
+  public function getMyValue(): int
+  {
+    return static::MY_VALUE;
+  }
+}
+```
+
+## Using `parent` with the Scope Resolution Operator
+
+There may be a need to specifically reference a constant, property or method available from the parent scope:
+
+```php
+class MyClass
+{
+  public function getMaximum(): int
+  {
+    return 5;
+  }
+}
+
+class AnotherClass extends MyClass
+{
+  public function getMaximum(): int
+  {
+    return parent::getMaximum() * 2;
+  }
+}
+
+// (new AnotherClass())->getMaximum() => 10
+```
+
+Most commonly in object oriented programming `parent` is used to call the call the parent constructor when an object is being instantiated:
+
+```php
+class ChildClass extends ParentClass
+{
+  public function __construct(): void
+  {
+    parent::__construct();
+  }
+}
+```
+
+## Caveats
+
+### Constant, Property, and Method Visibility
+
+The scope resolution operator still follows the rules set out by `public`, `private`, and `protected` visibility modifiers.

concepts/scope-resolution-operator/introduction.md

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+# Scope Resolution Operator
+
+The scope resolution operator (`::`) allows us to reference a class to access its name constants, static properties, or static methods.
+
+```php
+class MyClass
+{
+  public const MY_VALUE = 1;
+}
+
+// MyClass::class => "MyClass"
+// MyClass::MY_VALUE => 1
+```
+
+## Using `self` and `static` with the Scope Resolution Operator
+
+It may be required for an object to reference its own scope. To facilitate this, the `self` keyword allows a class to reference its own scope. Using the `self` keyword decouples the class from its own name -- making it easier to maintain code over time.
+
+```php
+class MyClass
+{
+  public const MY_VALUE = 1;
+
+  public function getMyValue(): int
+  {
+    return self::MY_VALUE;
+  }
+}
+
+// (new MyClass)->getMyValue() => 1
+```
+
+Use the `static` keyword with the scope resolution operator to "late bind" the reference to the current descendent class.
+
+```php
+// Update MyClass:
+class MyClass
+{
+  public const MY_VALUE = 1;
+
+  public function getMyValue(): int
+  {
+    return static::MY_VALUE;
+  }
+}
+```
+
+## Using `parent` with the Scope Resolution Operator
+
+The `parent` keyword is used to reference parent class constant, properties or methods, Commonly it is used to call the call the parent constructor when an object is being instantiated:
+
+```php
+class ChildClass extends ParentClass
+{
+  public function __construct(): void
+  {
+    parent::__construct();
+  }
+}
+```
+
+## Caveats
+
+### Constant, Property, and Method Visibility
+
+The scope resolution operator still follows the rules set out by `public`, `private`, and `protected` visibility modifiers.

concepts/scope-resolution-operator/links.json

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+[
+  {
+    "url": "https://www.php.net/manual/en/language.oop5.paamayim-nekudotayim.php",
+    "description": "Scope Resolution Operator (`::`)"
+  }
+]