docs(guide/directive): clarification on the 'matches' terminology

Closes #8120

Author: Izhaki

docs/content/guide/directive.ngdoc

@@ -43,18 +43,28 @@ mirrors the process of compiling source code in
 Before we can write a directive, we need to know how Angular's {@link guide/compiler HTML compiler}
 determines when to use a given directive.
 
-In the following example, we say that the `<input>` element **matches** the `ngModel` directive.
+Similar to the terminology used when an [element **matches** a selector]
+(https://developer.mozilla.org/en-US/docs/Web/API/Element.matches), we say an element **matches** a
+directive when the directive is part of its declaration.
+
+In the following example, we say that the `<input>` element **matches** the `ngModel` directive
 
 ```html
 <input ng-model="foo">
 ```
 
-The following also **matches** `ngModel`:
+The following `<input>` element also **matches** `ngModel`:
 
 ```html
 <input data-ng-model="foo">
 ```
 
+And the following <person> element **matches** the `person` directive:
+
+```html
+<person>{{name}}</person>
+```
+
 ### Normalization
 
 Angular **normalizes** an element's tag and attribute name to determine which elements match which