` or any other element with the
+ * `tooltip` selector,
+ * like so:
+ *
+ * ```
+ *
+ * ```
+ *
+ * Directives can also control the instantiation, destruction, and positioning of inline template
+ * elements:
+ *
+ * A directive uses a {@link ViewContainerRef} to instantiate, insert, move, and destroy views at
+ * runtime.
+ * The {@link ViewContainerRef} is created as a result of `
` element, and represents a
+ * location in the current view
+ * where these actions are performed.
+ *
+ * Views are always created as children of the current {@link ViewMetadata}, and as siblings of the
+ * `` element. Thus a
+ * directive in a child view cannot inject the directive that created it.
+ *
+ * Since directives that create views via ViewContainers are common in Angular, and using the full
+ * `` element syntax is wordy, Angular
+ * also supports a shorthand notation: `` and `` are
+ * equivalent.
+ *
+ * Thus,
+ *
+ * ```
+ *
+ * ```
+ *
+ * Expands in use to:
+ *
+ * ```
+ *
+ * ```
+ *
+ * Notice that although the shorthand places `*foo="bar"` within the `` element, the binding for
+ * the directive
+ * controller is correctly instantiated on the `` element rather than the `` element.
+ *
+ *
+ * ## Example
+ *
+ * Let's suppose we want to implement the `unless` behavior, to conditionally include a template.
+ *
+ * Here is a simple directive that triggers on an `unless` selector:
+ *
+ * ```
+ * @Directive({
+ * selector: '[unless]',
+ * properties: ['unless']
+ * })
+ * export class Unless {
+ * viewContainer: ViewContainerRef;
+ * templateRef: TemplateRef;
+ * prevCondition: boolean;
+ *
+ * constructor(viewContainer: ViewContainerRef, templateRef: TemplateRef) {
+ * this.viewContainer = viewContainer;
+ * this.templateRef = templateRef;
+ * this.prevCondition = null;
+ * }
+ *
+ * set unless(newCondition) {
+ * if (newCondition && (isBlank(this.prevCondition) || !this.prevCondition)) {
+ * this.prevCondition = true;
+ * this.viewContainer.clear();
+ * } else if (!newCondition && (isBlank(this.prevCondition) || this.prevCondition)) {
+ * this.prevCondition = false;
+ * this.viewContainer.create(this.templateRef);
+ * }
+ * }
+ * }
+ * ```
+ *
+ * We can then use this `unless` selector in a template:
+ * ```
+ *
+ * ```
+ *
+ * Once the directive instantiates the child view, the shorthand notation for the template expands
+ * and the result is:
+ *
+ * ```
+ *
+ * ```
+ *
+ * Note also that although the `` template still exists inside the ``,
+ * the instantiated
+ * view occurs on the second `` which is a sibling to the `` element.
+ */
+ class DirectiveMetadata extends InjectableMetadata {
+
+
+ /**
+ * The CSS selector that triggers the instantiation of a directive.
+ *
+ * Angular only allows directives to trigger on CSS selectors that do not cross element
+ * boundaries.
+ *
+ * `selector` may be declared as one of the following:
+ *
+ * - `element-name`: select by element name.
+ * - `.class`: select by class name.
+ * - `[attribute]`: select by attribute name.
+ * - `[attribute=value]`: select by attribute name and value.
+ * - `:not(sub_selector)`: select only if the element does not match the `sub_selector`.
+ * - `selector1, selector2`: select if either `selector1` or `selector2` matches.
+ *
+ *
+ * ## Example
+ *
+ * Suppose we have a directive with an `input[type=text]` selector.
+ *
+ * And the following HTML:
+ *
+ * ```html
+ *