# Doctype

Valid HTML and XHTML documents should include a `DOCTYPE` declaration. Besides being difficult
to remember, these can also affect how certain elements in your document should be rendered (for
instance, `CDATA` escaping in `<script>` and `<style>` elements.

The `Doctype` helper allows you to specify one of the following types:

- `XHTML11`
- `XHTML1_STRICT`
- `XHTML1_TRANSITIONAL`
- `XHTML1_FRAMESET`
- `XHTML1_RDFA`
- `XHTML1_RDFA11`
- `XHTML_BASIC1`
- `XHTML5`
- `HTML4_STRICT`
- `HTML4_LOOSE`
- `HTML4_FRAMESET`
- `HTML5`
- `CUSTOM_XHTML`
- `CUSTOM`

You can also specify a custom doctype as long as it is well-formed.

The `Doctype` helper is a concrete implementation of the
[Placeholder helper](placeholder.md).

## Basic Usage

You may specify the doctype at any time. However, helpers that depend on the
doctype for their output will recognize it only after you have set it, so the
easiest approach is to specify it in your bootstrap:

```php
use Zend\View\Helper\Doctype;

$doctypeHelper = new Doctype();
$doctypeHelper->doctype('XHTML1_STRICT');
```

And then print it out on top of your layout script:

```php
<?php echo $this->doctype() ?>
```

Within an application based off the [skeleton application](https://github.com/zendframework/ZendSkeletonApplication),
you can specify the doctype via configuration:

```php
// module/Application/config/module.config.php:
return [
    /* ... */
    'view_manager' => [
        'doctype' => 'html5',
        /* ... */
    ],
];
```

## Retrieving the Doctype

If you need to know the doctype, you can do so by calling `getDoctype()` on the
helper, which is returned by invoking the helper from the view.

```php
$doctype = $this->doctype()->getDoctype();
```

Typically, you'll want to know if the doctype is XHTML or not; for this, the
`isXhtml()` method will suffice:

```php
if ($this->doctype()->isXhtml()) {
    // do something differently
}
```

You can also check if the doctype represents an HTML5 document.

```php
if ($this->doctype()->isHtml5()) {
    // do something differently
}
```

## Choosing a Doctype to Use with the Open Graph Protocol

To implement the [Open Graph Protocol](http://opengraphprotocol.org/), you may
specify the `XHTML1_RDFA` doctype. This doctype allows a developer to use the
[Resource Description Framework](http://www.w3.org/TR/xhtml-rdfa-primer/) within
an XHTML document.

```php
use Zend\View\Helper\Doctype;

$doctypeHelper = new Doctype();
$doctypeHelper->doctype('XHTML1_RDFA');
```

The RDFa doctype allows XHTML to validate when the 'property' meta tag attribute
is used per the Open Graph Protocol spec. Example within a view script:

```php
<?= $this->doctype('XHTML1_RDFA'); ?>
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:og="http://opengraphprotocol.org/schema/">
<head>
   <meta property="og:type" content="musician" />
```

In the previous example, we set the property to `og:type`. The `og` references
the Open Graph namespace we specified in the html tag. The content identifies
the page as being about a musician. See the [Open Graph Protocol
documentation](http://opengraphprotocol.org/) for supported properties. The
[HeadMeta helper](head-meta.md) may be used to programmatically set these Open
Graph Protocol meta tags.

Here is how you check if the doctype is set to `XHTML1_RDFA`:

```php
<?= $this->doctype() ?>
<html xmlns="http://www.w3.org/1999/xhtml"
    <?php if ($view->doctype()->isRdfa()): ?>
      xmlns:og="http://opengraphprotocol.org/schema/"
      xmlns:fb="http://www.facebook.com/2008/fbml"
    <?php endif; ?>
>
```

## Zend MVC View Manager

If you're running a ZendMvc application, you should specify doctype via the
[ViewManager](https://docs.zendframework.com/zend-mvc/services/#viewmanager) service.
