> For the complete documentation index, see [llms.txt](https://docs.hivepress.io/developer-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.hivepress.io/developer-docs/framework/fields.md).

# Fields

In HivePress, field types are implemented as PHP classes with properties and methods that determine the validation and rendering of the field HTML. For example, the `Email` field type renders a text input that accepts email addresses only. You can use any of the existing field types in forms or even create a new one if required.

### Creating field types

If you are developing a custom HivePress [extension](/developer-docs/tutorials/create-a-custom-hivepress-extension.md), you may need to create a new field type. To do this, create a new `class-{field-type}.php` file (use lowercase letters, numbers, and hyphens only) in the `includes/fields` extension subdirectory and HivePress will load it automatically.

{% hint style="info" %}
It’s good practice to re-use the existing HivePress field types and avoid creating new ones if possible. For example, a new type may be required if you need a completely new UI element, or if it requires some custom logic.
{% endhint %}

Then, define the field type PHP class. The class name should be based on the file name but with underscores instead of hyphens and no lowercase restriction (e.g. `Foo_Bar` class for the `class-foo-bar.php` file). Pick a name that is unique enough to avoid conflicts with other HivePress field types.

```php
<?php
namespace HivePress\Fields;

use HivePress\Helpers as hp;

// Exit if accessed directly.
defined( 'ABSPATH' ) || exit;

class Foo_Bar extends Field {

	// Declare the field properties.
	protected $max_length;

	// Set the property defaults.
	public function __construct( $args = [] ) {
		$args = hp\merge_arrays(
			[
				'max_length' => 123,
			],
			$args
		);

		parent::__construct( $args );
	}

	// Do something after the field is loaded.
	protected function boot() {
		if ( $this->max_length ) {
			$attributes['maxlength'] = $this->max_length;
		}

		parent::boot();
	}

	// Normalize the field value.
	public function normalize() {
		parent::normalize();

		if ( ! is_null( $this->value ) ) {
			$this->value = trim( wp_unslash( $this->value ) );
		}
	}

	// Sanitize the field value.
	public function sanitize() {
		$this->value = sanitize_text_field( $this->value );
	}

	// Validate the field value.
	public function validate() {
		if ( parent::validate() && strlen( $this->value ) > $this->max_length ) {
			$this->add_errors( 'Custom error message' );
		}

		return ! $this->errors;
	}

	// Render the field HTML.
	public function render() {
		return '<input type="text" name="' . esc_attr( $this->name ) . '" value="' . esc_attr( $this->value ) . '" ' . hp\html_attributes( $this->attributes ) . '>';
	}
}

```

The code example above implements a field type that normalizes values by trimming whitespace and removing slashes, then sanitizes them by removing HTML and special characters, and finally validates values based on its `max_length` property (set to `123` by default). The field itself is rendered as an HTML input of `text` type.

Also, a custom field type can be based on another type's PHP class, allowing you to re-use its properties and methods without repeating the code:

```php
<?php
namespace HivePress\Fields;

use HivePress\Helpers as hp;

// Exit if accessed directly.
defined( 'ABSPATH' ) || exit;

class Foo_Bar extends Number {

	// Override properties and methods of Number type.
}

```

In the same way, you can create custom field types for your HivePress extension.

### Customizing field types

You can customize any of the existing field types using [hooks](https://hivepress.github.io/hook-reference/). For example, the code below changes the default date format for the `Date` field type.

```php
add_filter(
	'hivepress/v1/fields/date',
	function( $field ) {
		$field['display_format'] = 'F j, Y';

		return $field;
	}
);
```

Similarly, you can customize any field type in HivePress or its extensions.