# Creating Form Elements Using Zend_Form_Element

A form is made of elements that typically correspond to HTML form input. Zend_Form_Element encapsulates single form elements, with the following areas of responsibility:

- validation (is submitted data valid?)

  - capturing of validation error codes and messages

- filtering (how is the element escaped or normalized prior to validation and/or for output?)

- rendering (how is the element displayed?)

- metadata and attributes (what information further qualifies the element?)

The base class, Zend_Form_Element, has reasonable defaults for many cases, but it is best to extend the class for commonly used special purpose elements. Additionally, Zend Framework ships with a number of standard XHTML elements; you can read about them in the Standard Elements chapter.

## Plugin Loaders

Zend_Form_Element makes use of Zend_Loader_PluginLoader to allow developers to specify locations of alternate validators, filters, and decorators. Each has its own plugin loader associated with it, and general accessors are used to retrieve and modify each.

The following loader types are used with the various plugin loader methods: 'validate', 'filter', and 'decorator'. The type names are case insensitive.

The methods used to interact with plugin loaders are as follows:

- setPluginLoader($loader, $type): `$loader` is the plugin loader object itself, while `$type` is one of the types specified above. This sets the plugin loader for the given type to the newly specified loader object.

- getPluginLoader($type): retrieves the plugin loader associated with `$type`.

- addPrefixPath($prefix, $path, $type = null): adds a prefix/path association to the loader specified by `$type`. If `$type` is `NULL`, it will attempt to add the path to all loaders, by appending the prefix with each of "_Validate", "_Filter", and "_Decorator"; and appending the path with "Validate/", "Filter/", and "Decorator/". If you have all your extra form element classes under a common hierarchy, this is a convenience method for setting the base prefix for them.

- addPrefixPaths(array $spec): allows you to add many paths at once to one or more plugin loaders. It expects each array item to be an array with the keys 'path', 'prefix', and 'type'.

Custom validators, filters, and decorators are an easy way to share functionality between forms and to encapsulate custom functionality.

Custom Label

One common use case for plugins is to provide replacements for standard classes. For instance, if you want to provide a different implementation of the 'Label' decorator -- for instance, to always append a colon -- you could create your own 'Label' decorator with your own class prefix, and then add it to your prefix path.

Let's start with a custom Label decorator. We'll give it the class prefix "My_Decorator", and the class itself will be in the file "My/Decorator/Label.php".

    class My_Decorator_Label extends Zend_Form_Decorator_Abstract
    {
        protected $_placement = 'PREPEND';

        public function render($content)
        {
            if (null === ($element = $this->getElement())) {
                return $content;
            }
            if (!method_exists($element, 'getLabel')) {
                return $content;
            }

            $label = $element->getLabel() . ':';

            if (null === ($view = $element->getView())) {
                return $this->renderLabel($content, $label);
            }

            $label = $view->formLabel($element->getName(), $label);

            return $this->renderLabel($content, $label);
        }

        public function renderLabel($content, $label)
        {
            $placement = $this->getPlacement();
            $separator = $this->getSeparator();

            switch ($placement) {
                case 'APPEND':
                    return $content . $separator . $label;
                case 'PREPEND':
                default:
                    return $label . $separator . $content;
            }
        }
    }

Now we can tell the element to use this plugin path when looking for decorators:

    $element->addPrefixPath('My_Decorator', 'My/Decorator/', 'decorator');

Alternately, we can do that at the form level to ensure all decorators use this path:

    $form->addElementPrefixPath('My_Decorator', 'My/Decorator/', 'decorator');

After it added as in the example above, the 'My/Decorator/' path will be searched first to see if the decorator exists there when you add a decorator. As a result, 'My_Decorator_Label' will now be used when the 'Label' decorator is requested.

## Filters

It's often useful and/or necessary to perform some normalization on input prior to validation. For example, you may want to strip out all HTML, but run your validations on what remains to ensure the submission is valid. Or you may want to trim empty space surrounding input so that a StringLength validator will use the correct length of the input without counting leading or trailing whitespace characters. These operations may be performed using Zend_Filter. Zend_Form_Element has support for filter chains, allowing you to specify multiple, sequential filters. Filtering happens both during validation and when you retrieve the element value via getValue():

    $filtered = $element->getValue();

Filters may be added to the chain in two ways:

- passing in a concrete filter instance

- providing a short filter name

Let's see some examples:

    // Concrete filter instance:
    $element->addFilter(new Zend_Filter_Alnum());

    // Short filter name:
    $element->addFilter('Alnum');
    $element->addFilter('alnum');

Short names are typically the filter name minus the prefix. In the default case, this will mean minus the 'Zend_Filter_' prefix. The first letter can be upper-cased or lower-cased.

Using Custom Filter Classes

If you have your own set of filter classes, you can tell Zend_Form_Element about these using addPrefixPath(). For instance, if you have filters under the 'My_Filter' prefix, you can tell Zend_Form_Element about this as follows:

    $element->addPrefixPath('My_Filter', 'My/Filter/', 'filter');

(Recall that the third argument indicates which plugin loader on which to perform the action.)

If at any time you need the unfiltered value, use the getUnfilteredValue() method:

    $unfiltered = $element->getUnfilteredValue();

For more information on filters, see the Zend_Filter documentation.

Methods associated with filters include:

- addFilter($nameOfFilter, array $options = null)

- addFilters(array $filters)

- setFilters(array $filters) (overwrites all filters)

- getFilter($name) (retrieve a filter object by name)

- getFilters() (retrieve all filters)

- removeFilter($name) (remove filter by name)

- clearFilters() (remove all filters)

## Validators

If you subscribe to the security mantra of "filter input, escape output," you'll should use validator to filter input submitted with your form. In Zend_Form, each element includes its own validator chain, consisting of Zend_Validate_* validators.

Validators may be added to the chain in two ways:

- passing in a concrete validator instance

- providing a short validator name

Let's see some examples:

    // Concrete validator instance:
    $element->addValidator(new Zend_Validate_Alnum());

    // Short validator name:
    $element->addValidator('Alnum');
    $element->addValidator('alnum');

Short names are typically the validator name minus the prefix. In the default case, this will mean minus the 'Zend_Validate_' prefix. As is the case with filters, the first letter can be upper-cased or lower-cased.

Using Custom Validator Classes

If you have your own set of validator classes, you can tell Zend_Form_Element about these using addPrefixPath(). For instance, if you have validators under the 'My_Validator' prefix, you can tell Zend_Form_Element about this as follows:

    $element->addPrefixPath('My_Validator', 'My/Validator/', 'validate');

(Recall that the third argument indicates which plugin loader on which to perform the action.)

If failing a particular validation should prevent later validators from firing, pass boolean `TRUE` as the second parameter:

    $element->addValidator('alnum', true);

If you are using a string name to add a validator, and the validator class accepts arguments to the constructor, you may pass these to the third parameter of addValidator() as an array:

    $element->addValidator('StringLength', false, array(6, 20));

Arguments passed in this way should be in the order in which they are defined in the constructor. The above example will instantiate the Zend_Validate_StringLenth class with its `$min` and `$max` parameters:

    $validator = new Zend_Validate_StringLength(6, 20);

Providing Custom Validator Error Messages

Some developers may wish to provide custom error messages for a validator. The `$options` argument of the Zend_Form_Element::addValidator() method allows you to do so by providing the key 'messages' and mapping it to an array of key/value pairs for setting the message templates. You will need to know the error codes of the various validation error types for the particular validator.

A better option is to use a Zend_Translate_Adapter with your form. Error codes are automatically passed to the adapter by the default Errors decorator; you can then specify your own error message strings by setting up translations for the various error codes of your validators.

You can also set many validators at once, using addValidators(). The basic usage is to pass an array of arrays, with each array containing 1 to 3 values, matching the constructor of addValidator():

    $element->addValidators(array(
        array('NotEmpty', true),
        array('alnum'),
        array('stringLength', false, array(6, 20)),
    ));

If you want to be more verbose or explicit, you can use the array keys 'validator', 'breakChainOnFailure', and 'options':

    $element->addValidators(array(
        array(
            'validator'           => 'NotEmpty',
            'breakChainOnFailure' => true),
        array('validator' => 'alnum'),
        array(
            'validator' => 'stringLength',
            'options'   => array(6, 20)),
    ));

This usage is good for illustrating how you could then configure validators in a config file:

    element.validators.notempty.validator = "NotEmpty"
    element.validators.notempty.breakChainOnFailure = true
    element.validators.alnum.validator = "Alnum"
    element.validators.strlen.validator = "StringLength"
    element.validators.strlen.options.min = 6
    element.validators.strlen.options.max = 20

Notice that every item has a key, whether or not it needs one; this is a limitation of using configuration files -- but it also helps make explicit what the arguments are for. Just remember that any validator options must be specified in order.

To validate an element, pass the value to isValid():

    if ($element->isValid($value)) {
        // valid
    } else {
        // invalid
    }

Validation Operates On Filtered Values

Zend_Form_Element::isValid() filters values through the provided filter chain prior to validation. See the Filters section for more information.

Validation Context

Zend_Form_Element::isValid() supports an additional argument, `$context`. Zend_Form::isValid() passes the entire array of data being processed to `$context` when validating a form, and Zend_Form_Element::isValid(), in turn, passes it to each validator. This means you can write validators that are aware of data passed to other form elements. As an example, consider a standard registration form that has fields for both password and a password confirmation; one validation would be that the two fields match. Such a validator might look like the following:

    class My_Validate_PasswordConfirmation extends Zend_Validate_Abstract
    {
        const NOT_MATCH = 'notMatch';

        protected $_messageTemplates = array(
            self::NOT_MATCH => 'Password confirmation does not match'
        );

        public function isValid($value, $context = null)
        {
            $value = (string) $value;
            $this->_setValue($value);

            if (is_array($context)) {
                if (isset($context['password_confirm'])
                    && ($value == $context['password_confirm']))
                {
                    return true;
                }
            } elseif (is_string($context) && ($value == $context)) {
                return true;
            }

            $this->_error(self::NOT_MATCH);
            return false;
        }
    }

Validators are processed in order. Each validator is processed, unless a validator created with a `TRUE` `$breakChainOnFailure` value fails its validation. Be sure to specify your validators in a reasonable order.

After a failed validation, you can retrieve the error codes and messages from the validator chain:

    $errors   = $element->getErrors();
    $messages = $element->getMessages();

(Note: error messages returned are an associative array of error code / error message pairs.)

In addition to validators, you can specify that an element is required, using setRequired($flag). By default, this flag is `FALSE`. In combination with setAllowEmpty($flag) (`TRUE` by default) and setAutoInsertNotEmptyValidator($flag) (`TRUE` by default), the behavior of your validator chain can be modified in a number of ways:

- Using the defaults, validating an Element without passing a value, or passing an empty string for it, skips all validators and validates to `TRUE`.

- setAllowEmpty(false) leaving the two other mentioned flags untouched, will validate against the validator chain you defined for this Element, regardless of the value passed to isValid().

- setRequired(true) leaving the two other mentioned flags untouched, will add a 'NotEmpty' validator on top of the validator chain (if none was already set)), with the `$breakChainOnFailure` flag set. This behavior lends required flag semantic meaning: if no value is passed, we immediately invalidate the submission and notify the user, and prevent other validators from running on what we already know is invalid data.

  If you do not want this behavior, you can turn it off by passing a `FALSE` value to setAutoInsertNotEmptyValidator($flag); this will prevent isValid() from placing the 'NotEmpty' validator in the validator chain.

For more information on validators, see the Zend_Validate documentation.

Using Zend_Form_Elements as general-purpose validators

Zend_Form_Element implements Zend_Validate_Interface, meaning an element may also be used as a validator in other, non-form related validation chains.

When is an element detected as empty?

As mentioned the 'NotEmpty' validator is used to detect if an element is empty or not. But Zend_Validate_NotEmpty does, per default, not work like PHP's method empty().

This means when an element contains an integer 0 or an string '0' then the element will be seen as not empty. If you want to have a different behaviour you must create your own instance of Zend_Validate_NotEmpty. There you can define the behaviour of this validator. See Zend_Validate_NotEmpty for details.

Methods associated with validation include:

- setRequired($flag) and isRequired() allow you to set and retrieve the status of the 'required' flag. When set to boolean `TRUE`, this flag requires that the element be in the data processed by Zend_Form.

- setAllowEmpty($flag) and getAllowEmpty() allow you to modify the behaviour of optional elements (i.e., elements where the required flag is `FALSE`). When the 'allow empty' flag is `TRUE`, empty values will not be passed to the validator chain.

- setAutoInsertNotEmptyValidator($flag) allows you to specify whether or not a 'NotEmpty' validator will be prepended to the validator chain when the element is required. By default, this flag is `TRUE`.

- addValidator($nameOrValidator, $breakChainOnFailure = false, array $options = null)

- addValidators(array $validators)

- setValidators(array $validators) (overwrites all validators)

- getValidator($name) (retrieve a validator object by name)

- getValidators() (retrieve all validators)

- removeValidator($name) (remove validator by name)

- clearValidators() (remove all validators)

### Custom Error Messages

At times, you may want to specify one or more specific error messages to use instead of the error messages generated by the validators attached to your element. Additionally, at times you may want to mark the element invalid yourself. As of 1.6.0, this functionality is possible via the following methods.

- addErrorMessage($message): add an error message to display on form validation errors. You may call this more than once, and new messages are appended to the stack.

- addErrorMessages(array $messages): add multiple error messages to display on form validation errors.

- setErrorMessages(array $messages): add multiple error messages to display on form validation errors, overwriting all previously set error messages.

- getErrorMessages(): retrieve the list of custom error messages that have been defined.

- clearErrorMessages(): remove all custom error messages that have been defined.

- markAsError(): mark the element as having failed validation.

- hasErrors(): determine whether the element has either failed validation or been marked as invalid.

- addError($message): add a message to the custom error messages stack and flag the element as invalid.

- addErrors(array $messages): add several messages to the custom error messages stack and flag the element as invalid.

- setErrors(array $messages): overwrite the custom error messages stack with the provided messages and flag the element as invalid.

All errors set in this fashion may be translated. Additionally, you may insert the placeholder "%value%" to represent the element value; this current element value will be substituted when the error messages are retrieved.

## Decorators

One particular pain point for many web developers is the creation of the XHTML forms themselves. For each element, the developer needs to create markup for the element itself (typically a label) and special markup for displaying validation error messages. The more elements on the page, the less trivial this task becomes.

Zend_Form_Element tries to solve this issue through the use of "decorators". Decorators are simply classes that have access to the element and a method for rendering content. For more information on how decorators work, please see the section on Zend_Form_Decorator.

The default decorators used by Zend_Form_Element are:

- ViewHelper: specifies a view helper to use to render the element. The 'helper' element attribute can be used to specify which view helper to use. By default, Zend_Form_Element specifies the 'formText' view helper, but individual subclasses specify different helpers.

- Errors: appends error messages to the element using Zend_View_Helper_FormErrors. If none are present, nothing is appended.

- Description: appends the element description. If none is present, nothing is appended. By default, the description is rendered in a <p> tag with a class of 'description'.

- HtmlTag: wraps the element and errors in an HTML <dd> tag.

- Label: prepends a label to the element using Zend_View_Helper_FormLabel, and wraps it in a <dt> tag. If no label is provided, just the definition term tag is rendered.

Default Decorators Do Not Need to Be Loaded

By default, the default decorators are loaded during object initialization. You can disable this by passing the 'disableLoadDefaultDecorators' option to the constructor:

    $element = new Zend_Form_Element('foo',
                                     array('disableLoadDefaultDecorators' =>
                                          true)
                                    );

This option may be mixed with any other options you pass, both as array options or in a Zend_Config object.

Since the order in which decorators are registered matters- the first decorator registered is executed first- you will need to make sure you register your decorators in an appropriate order, or ensure that you set the placement options in a sane fashion. To give an example, here is the code that registers the default decorators:

    $this->addDecorators(array(
        array('ViewHelper'),
        array('Errors'),
        array('Description', array('tag' => 'p', 'class' => 'description')),
        array('HtmlTag', array('tag' => 'dd')),
        array('Label', array('tag' => 'dt')),
    ));

The initial content is created by the 'ViewHelper' decorator, which creates the form element itself. Next, the 'Errors' decorator fetches error messages from the element, and, if any are present, passes them to the 'FormErrors' view helper to render. If a description is present, the 'Description' decorator will append a paragraph of class 'description' containing the descriptive text to the aggregated content. The next decorator, 'HtmlTag', wraps the element, errors, and description in an HTML <dd> tag. Finally, the last decorator, 'label', retrieves the element's label and passes it to the 'FormLabel' view helper, wrapping it in an HTML <dt> tag; the value is prepended to the content by default. The resulting output looks basically like this:

    <dt><label for="foo" class="optional">Foo</label></dt>
    <dd>
        <input type="text" name="foo" id="foo" value="123" />
        <ul class="errors">
            <li>"123" is not an alphanumeric value</li>
        </ul>
        <p class="description">
            This is some descriptive text regarding the element.
        </p>
    </dd>

For more information on decorators, read the Zend_Form_Decorator section.

Using Multiple Decorators of the Same Type

Internally, Zend_Form_Element uses a decorator's class as the lookup mechanism when retrieving decorators. As a result, you cannot register multiple decorators of the same type; subsequent decorators will simply overwrite those that existed before.

To get around this, you can use aliases. Instead of passing a decorator or decorator name as the first argument to addDecorator(), pass an array with a single element, with the alias pointing to the decorator object or name:

    // Alias to 'FooBar':
    $element->addDecorator(array('FooBar' => 'HtmlTag'),
                           array('tag' => 'div'));

    // And retrieve later:
    $decorator = $element->getDecorator('FooBar');

In the addDecorators() and setDecorators() methods, you will need to pass the 'decorator' option in the array representing the decorator:

    // Add two 'HtmlTag' decorators, aliasing one to 'FooBar':
    $element->addDecorators(
        array('HtmlTag', array('tag' => 'div')),
        array(
            'decorator' => array('FooBar' => 'HtmlTag'),
            'options' => array('tag' => 'dd')
        ),
    );

    // And retrieve later:
    $htmlTag = $element->getDecorator('HtmlTag');
    $fooBar  = $element->getDecorator('FooBar');

Methods associated with decorators include:

- addDecorator($nameOrDecorator, array $options = null)

- addDecorators(array $decorators)

- setDecorators(array $decorators) (overwrites all decorators)

- getDecorator($name) (retrieve a decorator object by name)

- getDecorators() (retrieve all decorators)

- removeDecorator($name) (remove decorator by name)

- clearDecorators() (remove all decorators)

Zend_Form_Element also uses overloading to allow rendering specific decorators. __call() will intercept methods that lead with the text 'render' and use the remainder of the method name to lookup a decorator; if found, it will then render that single decorator. Any arguments passed to the method call will be used as content to pass to the decorator's render() method. As an example:

    // Render only the ViewHelper decorator:
    echo $element->renderViewHelper();

    // Render only the HtmlTag decorator, passing in content:
    echo $element->renderHtmlTag("This is the html tag content");

If the decorator does not exist, an exception is raised.

## Metadata and Attributes

Zend_Form_Element handles a variety of attributes and element metadata. Basic attributes include:

- name: the element name. Uses the setName() and getName() accessors.

- label: the element label. Uses the setLabel() and getLabel() accessors.

- order: the index at which an element should appear in the form. Uses the setOrder() and getOrder() accessors.

- value: the current element value. Uses the setValue() and getValue() accessors.

- description: a description of the element; often used to provide tooltip or javascript contextual hinting describing the purpose of the element. Uses the setDescription() and getDescription() accessors.

- required: flag indicating whether or not the element is required when performing form validation. Uses the setRequired() and getRequired() accessors. This flag is `FALSE` by default.

- allowEmpty: flag indicating whether or not a non-required (optional) element should attempt to validate empty values. If it is set to `TRUE` and the required flag is `FALSE`, empty values are not passed to the validator chain and are presumed `TRUE`. Uses the setAllowEmpty() and getAllowEmpty() accessors. This flag is `TRUE` by default.

- autoInsertNotEmptyValidator: flag indicating whether or not to insert a 'NotEmpty' validator when the element is required. By default, this flag is `TRUE`. Set the flag with setAutoInsertNotEmptyValidator($flag) and determine the value with autoInsertNotEmptyValidator().

Form elements may require additional metadata. For XHTML form elements, for instance, you may want to specify attributes such as the class or id. To facilitate this are a set of accessors:

- setAttrib($name, $value): add an attribute

- setAttribs(array $attribs): like addAttribs(), but overwrites

- getAttrib($name): retrieve a single attribute value

- getAttribs(): retrieve all attributes as key/value pairs

Most of the time, however, you can simply access them as object properties, as Zend_Form_Element utilizes overloading to facilitate access to them:

    // Equivalent to $element->setAttrib('class', 'text'):
    $element->class = 'text;

By default, all attributes are passed to the view helper used by the element during rendering, and rendered as HTML attributes of the element tag.

## Standard Elements

Zend_Form ships with a number of standard elements; please read the Standard Elements chapter for full details.

## Zend_Form_Element Methods

Zend_Form_Element has many, many methods. What follows is a quick summary of their signatures, grouped by type:

- Configuration:

  - setOptions(array $options)

  - setConfig(Zend_Config $config)

- I18n:

  - setTranslator(Zend_Translate_Adapter $translator = null)

  - getTranslator()

  - setDisableTranslator($flag)

  - translatorIsDisabled()

- Properties:

  - setName($name)

  - getName()

  - setValue($value)

  - getValue()

  - getUnfilteredValue()

  - setLabel($label)

  - getLabel()

  - setDescription($description)

  - getDescription()

  - setOrder($order)

  - getOrder()

  - setRequired($flag)

  - getRequired()

  - setAllowEmpty($flag)

  - getAllowEmpty()

  - setAutoInsertNotEmptyValidator($flag)

  - autoInsertNotEmptyValidator()

  - setIgnore($flag)

  - getIgnore()

  - getType()

  - setAttrib($name, $value)

  - setAttribs(array $attribs)

  - getAttrib($name)

  - getAttribs()

- Plugin loaders and paths:

  - setPluginLoader(Zend_Loader_PluginLoader_Interface $loader, $type)

  - getPluginLoader($type)

  - addPrefixPath($prefix, $path, $type = null)

  - addPrefixPaths(array $spec)

- Validation:

  - addValidator($validator, $breakChainOnFailure = false, $options = array())

  - addValidators(array $validators)

  - setValidators(array $validators)

  - getValidator($name)

  - getValidators()

  - removeValidator($name)

  - clearValidators()

  - isValid($value, $context = null)

  - getErrors()

  - getMessages()

- Filters:

  - addFilter($filter, $options = array())

  - addFilters(array $filters)

  - setFilters(array $filters)

  - getFilter($name)

  - getFilters()

  - removeFilter($name)

  - clearFilters()

- Rendering:

  - setView(Zend_View_Interface $view = null)

  - getView()

  - addDecorator($decorator, $options = null)

  - addDecorators(array $decorators)

  - setDecorators(array $decorators)

  - getDecorator($name)

  - getDecorators()

  - removeDecorator($name)

  - clearDecorators()

  - render(Zend_View_Interface $view = null)

## Configuration

Zend_Form_Element's constructor accepts either an array of options or a Zend_Config object containing options, and it can also be configured using either setOptions() or setConfig(). Generally speaking, keys are named as follows:

- If 'set' + key refers to a Zend_Form_Element method, then the value provided will be passed to that method.

- Otherwise, the value will be used to set an attribute.

Exceptions to the rule include the following:

- prefixPath will be passed to addPrefixPaths()

- The following setters cannot be set in this way:

  - setAttrib (though setAttribs will work)

  - setConfig

  - setOptions

  - setPluginLoader

  - setTranslator

  - setView

As an example, here is a config file that passes configuration for every type of configurable data:

    [element]
    name = "foo"
    value = "foobar"
    label = "Foo:"
    order = 10
    required = true
    allowEmpty = false
    autoInsertNotEmptyValidator = true
    description = "Foo elements are for examples"
    ignore = false
    attribs.id = "foo"
    attribs.class = "element"
    ; For radio button elements
    escape = true
    listsep = "<br />\n"
    ; sets 'onclick' attribute
    onclick = "autoComplete(this, '/form/autocomplete/element')"
    prefixPaths.decorator.prefix = "My_Decorator"
    prefixPaths.decorator.path = "My/Decorator/"
    disableTranslator = 0
    validators.required.validator = "NotEmpty"
    validators.required.breakChainOnFailure = true
    validators.alpha.validator = "alpha"
    validators.regex.validator = "regex"
    validators.regex.options.pattern = "/^[A-F].*/$"
    filters.ucase.filter = "StringToUpper"
    decorators.element.decorator = "ViewHelper"
    decorators.element.options.helper = "FormText"
    decorators.label.decorator = "Label"

## Custom Elements

You can create your own custom elements by simply extending the Zend_Form_Element class. Common reasons to do so include:

- Elements that share common validators and/or filters

- Elements that have custom decorator functionality

There are two methods typically used to extend an element: init(), which can be used to add custom initialization logic to your element, and loadDefaultDecorators(), which can be used to set a list of default decorators used by your element.

As an example, let's say that all text elements in a form you are creating need to be filtered with StringTrim, validated with a common regular expression, and that you want to use a custom decorator you've created for displaying them, 'My_Decorator_TextItem'. In addition, you have a number of standard attributes, including 'size', 'maxLength', and 'class' you wish to specify. You could define an element to accomplish this as follows:

    class My_Element_Text extends Zend_Form_Element
    {
        public function init()
        {
            $this->addPrefixPath('My_Decorator', 'My/Decorator/', 'decorator')
                 ->addFilters('StringTrim')
                 ->addValidator('Regex', false, array('/^[a-z0-9]{6,}$/i'))
                 ->addDecorator('TextItem')
                 ->setAttrib('size', 30)
                 ->setAttrib('maxLength', 45)
                 ->setAttrib('class', 'text');
        }
    }

You could then inform your form object about the prefix path for such elements, and start creating elements:

    $form->addPrefixPath('My_Element', 'My/Element/', 'element')
         ->addElement('text', 'foo');

The 'foo' element will now be of type My_Element_Text, and exhibit the behaviour you've outlined.

Another method you may want to override when extending Zend_Form_Element is the loadDefaultDecorators() method. This method conditionally loads a set of default decorators for your element; you may wish to substitute your own decorators in your extending class:

    class My_Element_Text extends Zend_Form_Element
    {
        public function loadDefaultDecorators()
        {
            $this->addDecorator('ViewHelper')
                 ->addDecorator('DisplayError')
                 ->addDecorator('Label')
                 ->addDecorator('HtmlTag',
                                array('tag' => 'div', 'class' => 'element'));
        }
    }

There are many ways to customize elements. Read the API documentation of Zend_Form_Element to learn about all of the available methods.