new batch of docs

docs/content/guide/dev_guide.compiler.directives.ngdoc

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+@workInProgress
+@ngdoc overview
+@name Developer Guide: Angular HTML Compiler: Understanding Angular Directives
+@description
+
+
+An angular directive is a custom HTML attribute that angular knows how to process.  You add them to
+a template element like any other attribute.  Angular directives all have a `ng:` prefix.  In the
+following example, the angular directive (`ng:controller`) is  a div tag:
+
+
+        <div ng:controller>
+
+
+You use angular directives to modify DOM element properties. The element you modify can be an
+existing HTML element type or a custom DOM element type that you created. You can use any number of
+directives per element.
+
+
+You add angular directives to a standard HTML tag as in the following example, in which we have
+added the {@link api/angular.directive.ng:click ng:click} directive to a button tag:
+
+
+        <button name="button1" ng:click="foo()">Click This</button>
+
+
+In the example above, `name` is the standard HTML attribute, and `ng:click` is the angular
+directive. The `ng:click` directive lets you implement custom behavior in an associated controller
+function.
+
+
+In the next example, we add the {@link api/angular.directive.ng:bind ng:bind} directive to a
+`<span>` tag:
+
+
+        <span ng:bind="1+2"></span>
+
+
+The `ng:bind` directive tells angular to set up {@link dev_guide.templates.databinding data
+binding} between the data model and the view for the specified expression.  When the angular {@link
+dev_guide.compiler compiler} encounters an `ng:bind` directive in a template, it passes the
+attribute value to the `ng:bind` function, which in turn sets up the data binding. On any change to
+the expression in the model, the view is updated to display the span text with the changed
+expression value.
+
+
+
+
+## Related Topics
+
+
+* {@link dev_guide.compiler Angular HTML Compiler}
+* {@link dev_guide.compiler.directives.creating_directives Creating Angular Directives}
+* {@link dev_guide.compiler.directives_widgets Comparing Directives and Widgets}
+
+
+## Related API:
+
+
+* {@link api/angular.directive Directive API}
+* {@link api/angular.widget Widget API}