# Developer Guide: Angular HTML Compiler: Understanding Angular Markup

Work in Progress This page is currently being revised. It might be incomplete or contain inaccuracies.

Markup in angular is a feature that you can use in templates to transform the content of DOM elements prior to the compile phase (in which elements are compiled and link functions are returned. See the compiler docs for details on how the compiler works.) The ability to make pre-compile changes to DOM elements lets you create shorthand for `widget` and `directive` declarations.

Angular provides one built-in markup feature: the double curly-braces used to declare binding points (between the model and view) for angular expressions. You can also create your own custom markup.

## Using Double Curly-brace Markup (`{{ }}`)

The double curly-brace (`{{ }}`) markup translates an enclosed expression into an `ng:bind` directive:

    {{expression}}

is transformed to:

    <span ng:bind="expression"></span>

Markup is useful for the simple reason that `{{1+2}}` is easier to write and understand than `<span ng:bind="1+2"></span>`. After markup shorthand is expanded into the DOM elements it represents, the expanded elements are then compiled normally.

## Creating Custom Markup

Let's say you want to define markup that transforms `---` into a horizontal rule (`<hr/>`):

    header
    ---
    footer

should translate to:

    header
    <hr/>
    footer

Here is how you could extend the angular compiler to create the "---" markup:

    angular.markup('---', function(text, textNode, parentElement) {
        var compiler = this;
        var index = text.indexOf('---');
        if (index > -1) {
            textNode.after(text.substring(index + 3));
            textNode.after(angular.element('<hr>'));
            textNode.after(text.substring(0, index));
            textNode.remove();
        }
    });

Unlike the way the compiler processes `widgets` and `directives` (matching the name of the handler function to a DOM element or attribute name), the compiler calls every markup handler for every text node, giving the handler a chance to transform the text. The markup handler needs to find all the matches in the text.

### Attribute Markup

Attribute markup extends the angular compiler in a very similar way to markup, except that it allows you to modify the state of attribute text rather then the content of a node.

    angular.attrMarkup('extraClass', function(attrValue, attrName, element){
     if (attrName == 'additional-class') {
       element.addClass(attrValue);
     }
    });

### Related Topics

- Angular HTML Compiler

### Related API

- `Compiler API Reference`