repo_zf1/documentation/manual/en/module_specs/Zend_Form-Elements.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- Reviewed: no -->
<sect1 id="zend.form.elements">
    <title>Creating Form Elements Using Zend_Form_Element</title>

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

    <itemizedlist>
        <listitem>
            <para>
                validation (is submitted data valid?)
            </para>

            <itemizedlist>
                <listitem><para>capturing of validation error codes and messages</para></listitem>
            </itemizedlist>
        </listitem>

        <listitem><para>
            filtering (how is the element escaped or normalized prior to
            validation and/or for output?)
        </para></listitem>

        <listitem><para>
            rendering (how is the element displayed?)
        </para></listitem>

        <listitem><para>
            metadata and attributes (what information further qualifies the element?)
        </para></listitem>
    </itemizedlist>

    <para>
        The base class, <classname>Zend_Form_Element</classname>, 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 <link
            linkend="zend.form.standardElements">in the Standard Elements
            chapter</link>.
    </para>

    <sect2 id="zend.form.elements.loaders">
        <title>Plugin Loaders</title>

        <para>
            <classname>Zend_Form_Element</classname> makes use of <link
                linkend="zend.loader.pluginloader">Zend_Loader_PluginLoader</link>
            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.
        </para>

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

        <para>
            The methods used to interact with plugin loaders are as follows:
        </para>

        <itemizedlist>
            <listitem><para>
                <code>setPluginLoader($loader, $type)</code>:
                <code>$loader</code> is the plugin loader object itself, while
                <code>$type</code> is one of the types specified above. This
                sets the plugin loader for the given type to the newly
                specified loader object.
            </para></listitem>

            <listitem><para>
                <code>getPluginLoader($type)</code>: retrieves the plugin
                loader associated with <code>$type</code>.
            </para></listitem>

            <listitem><para>
                <code>addPrefixPath($prefix, $path, $type = null)</code>: adds
                a prefix/path association to the loader specified by
                <code>$type</code>. If <code>$type</code> 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.
            </para></listitem>

            <listitem><para>
                <code>addPrefixPaths(array $spec)</code>: 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'.
            </para></listitem>
        </itemizedlist>

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

        <example id="zend.form.elements.loaders.customLabel">
            <title>Custom Label</title>

            <para>
                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.
            </para>

            <para>
                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".
            </para>

            <programlisting role="php"><![CDATA[
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;
        }
    }
}
]]></programlisting>

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

            <programlisting role="php"><![CDATA[
$element->addPrefixPath('My_Decorator', 'My/Decorator/', 'decorator');
]]></programlisting>

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

            <programlisting role="php"><![CDATA[
$form->addElementPrefixPath('My_Decorator', 'My/Decorator/', 'decorator');
]]></programlisting>

            <para>
                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.
            </para>
        </example>
    </sect2>

    <sect2 id="zend.form.elements.filters">
        <title>Filters</title>

        <para>
            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
            <classname>Zend_Filter</classname>. <classname>Zend_Form_Element</classname> 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
            <code>getValue()</code>:
        </para>

        <programlisting role="php"><![CDATA[
$filtered = $element->getValue();

]]></programlisting>

        <para>
            Filters may be added to the chain in two ways:
        </para>

        <itemizedlist>
            <listitem><para>
                passing in a concrete filter instance
            </para></listitem>

            <listitem><para>
                providing a filter name – either a short name or fully
                qualified class name
            </para></listitem>
        </itemizedlist>

        <para>
            Let's see some examples:
        </para>

        <programlisting role="php"><![CDATA[
// Concrete filter instance:
$element->addFilter(new Zend_Filter_Alnum());

// Fully qualified class name:
$element->addFilter('Zend_Filter_Alnum');

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

        <para>
            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.
        </para>

        <note>
            <title>Using Custom Filter Classes</title>

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

            <programlisting role="php"><![CDATA[
$element->addPrefixPath('My_Filter', 'My/Filter/', 'filter');
]]></programlisting>

            <para>
                (Recall that the third argument indicates which plugin loader
                on which to perform the action.)
            </para>
        </note>

        <para>
            If at any time you need the unfiltered value, use the
            <code>getUnfilteredValue()</code> method:
        </para>

        <programlisting role="php"><![CDATA[
$unfiltered = $element->getUnfilteredValue();
]]></programlisting>

        <para>
            For more information on filters, see the <link
                linkend="zend.filter.introduction">Zend_Filter
                documentation</link>.
        </para>

        <para>
            Methods associated with filters include:
        </para>

        <itemizedlist>
            <listitem><para>
                <code>addFilter($nameOfFilter, array $options = null)</code>
            </para></listitem>

            <listitem><para>
                <code>addFilters(array $filters)</code>
            </para></listitem>

            <listitem><para>
                <code>setFilters(array $filters)</code> (overwrites all filters)
            </para></listitem>

            <listitem><para>
                <code>getFilter($name)</code> (retrieve a filter object by name)
            </para></listitem>

            <listitem><para>
                <code>getFilters()</code> (retrieve all filters)
            </para></listitem>

            <listitem><para>
                <code>removeFilter($name)</code> (remove filter by name)
            </para></listitem>

            <listitem><para>
                <code>clearFilters()</code> (remove all filters)
            </para></listitem>
        </itemizedlist>
    </sect2>

    <sect2 id="zend.form.elements.validators">
        <title>Validators</title>

        <para>
            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 <classname>Zend_Form</classname>, each element includes its own validator
            chain, consisting of <classname>Zend_Validate_*</classname> validators.
        </para>

        <para>
            Validators may be added to the chain in two ways:
        </para>

        <itemizedlist>
            <listitem><para>
                passing in a concrete validator instance
            </para></listitem>

            <listitem><para>
                providing a validator name – either a short name or fully
                qualified class name
            </para></listitem>
        </itemizedlist>

        <para>
            Let's see some examples:
        </para>

        <programlisting role="php"><![CDATA[
// Concrete validator instance:
$element->addValidator(new Zend_Validate_Alnum());

// Fully qualified class name:
$element->addValidator('Zend_Validate_Alnum');

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

        <para>
            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.
        </para>

        <note>
            <title>Using Custom Validator Classes</title>

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

            <programlisting role="php"><![CDATA[
$element->addPrefixPath('My_Validator', 'My/Validator/', 'validate');
]]></programlisting>

            <para>
                (Recall that the third argument indicates which plugin loader
                on which to perform the action.)
            </para>
        </note>

        <para>
            If failing a particular validation should prevent later validators
            from firing, pass boolean <code>true</code> as the second parameter:
        </para>

        <programlisting role="php"><![CDATA[
$element->addValidator('alnum', true);
]]></programlisting>

        <para>
            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 <code>addValidator()</code> as an
            array:
        </para>

        <programlisting role="php"><![CDATA[
$element->addValidator('StringLength', false, array(6, 20));
]]></programlisting>

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

        <programlisting role="php"><![CDATA[
$validator = new Zend_Validate_StringLength(6, 20);
]]></programlisting>

        <note>
            <title>Providing Custom Validator Error Messages</title>

            <para>
                Some developers may wish to provide custom error messages for a
                validator. The <code>$options</code> argument of the <classname>Zend_Form_Element::addValidator()</classname> 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.
            </para>

            <para>
                A better option is to use a <classname>Zend_Translate_Adapter</classname>
                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.
            </para>
        </note>

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

        <programlisting role="php"><![CDATA[
$element->addValidators(array(
    array('NotEmpty', true),
    array('alnum'),
    array('stringLength', false, array(6, 20)),
));
]]></programlisting>

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

        <programlisting role="php"><![CDATA[
$element->addValidators(array(
    array(
        'validator'           => 'NotEmpty',
        'breakChainOnFailure' => true),
    array('validator' => 'alnum'),
    array(
        'validator' => 'stringLength',
        'options'   => array(6, 20)),
));
]]></programlisting>

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

        <programlisting role="ini"><![CDATA[
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
]]></programlisting>

        <para>
            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.
        </para>

        <para>
            To validate an element, pass the value to
            <code>isValid()</code>:
        </para>

        <programlisting role="php"><![CDATA[
if ($element->isValid($value)) {
    // valid
} else {
    // invalid
}
]]></programlisting>

        <note>
            <title>Validation Operates On Filtered Values</title>

            <para>
                <classname>Zend_Form_Element::isValid()</classname> filters values through
                the provided filter chain prior to validation. See <link
                    linkend="zend.form.elements.filters">the Filters
                    section</link> for more information.
            </para>
        </note>

        <note>
            <title>Validation Context</title>

            <para>
                <classname>Zend_Form_Element::isValid()</classname> supports an
                additional argument, <code>$context</code>.
                <classname>Zend_Form::isValid()</classname> passes the entire array of
                data being processed to <code>$context</code> when validating a
                form, and <classname>Zend_Form_Element::isValid()</classname>, 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:
            </para>

            <programlisting role="php"><![CDATA[
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;
    }
}
]]></programlisting>
        </note>

        <para>
            Validators are processed in order. Each validator is processed,
            unless a validator created with a true
            <code>breakChainOnFailure</code> value fails its validation. Be
            sure to specify your validators in a reasonable order.
        </para>

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

        <programlisting role="php"><![CDATA[
$errors   = $element->getErrors();
$messages = $element->getMessages();
]]></programlisting>

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

        <para>
            In addition to validators, you can specify that an element is
            required, using <code>setRequired(true)</code>. By default, this
            flag is false, meaning that your validator chain will be skipped if
            no value is passed to <code>isValid()</code>. You can modify this
            behavior in a number of ways:
        </para>

        <itemizedlist>
            <listitem>
                <para>
                    By default, when an element is required, a flag,
                    'allowEmpty', is also true. This means that if a value
                    evaluating to empty is passed to <code>isValid()</code>, the
                    validators will be skipped. You can toggle this flag using
                    the accessor <code>setAllowEmpty($flag)</code>; when the
                    flag is false and a value is passed, the validators
                    will still run.
                </para>
            </listitem>

            <listitem>
                <para>
                    By default, if an element is required but does not contain
                    a 'NotEmpty' validator, <code>isValid()</code> will add one
                    to the top of the stack, with the
                    <code>breakChainOnFailure</code> 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.
                </para>

                <para>
                    If you do not want this behavior, you can turn it off by
                    passing a false value to
                    <code>setAutoInsertNotEmptyValidator($flag)</code>; this
                    will prevent <code>isValid()</code> from placing the
                    'NotEmpty' validator in the validator chain.
                </para>
            </listitem>
        </itemizedlist>

        <para>
            For more information on validators, see the <link
                linkend="zend.validate.introduction">Zend_Validate
                documentation</link>.
        </para>

        <note>
            <title>Using Zend_Form_Elements as general-purpose validators</title>

            <para>
                <classname>Zend_Form_Element</classname> implements
                <classname>Zend_Validate_Interface</classname>, meaning an element may
                also be used as a validator in other, non-form related
                validation chains.
            </para>
        </note>

        <para>
            Methods associated with validation include:
        </para>

        <itemizedlist>
            <listitem><para>
                    <code>setRequired($flag)</code> and
                    <code>isRequired()</code> allow you to set and retrieve the
                    status of the 'required' flag. When set to boolean <code>true</code>, this
                    flag requires that the element be in the data processed by
                    <classname>Zend_Form</classname>.
            </para></listitem>

            <listitem><para>
                    <code>setAllowEmpty($flag)</code> and
                    <code>getAllowEmpty()</code> 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.
            </para></listitem>

            <listitem><para>
                    <code>setAutoInsertNotEmptyValidator($flag)</code> 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.
            </para></listitem>

            <listitem><para>
                <code>addValidator($nameOrValidator, $breakChainOnFailure = false, array $options = null)</code>
            </para></listitem>

            <listitem><para>
                <code>addValidators(array $validators)</code>
            </para></listitem>

            <listitem><para>
                <code>setValidators(array $validators)</code> (overwrites all validators)
            </para></listitem>

            <listitem><para>
                <code>getValidator($name)</code> (retrieve a validator object by name)
            </para></listitem>

            <listitem><para>
                <code>getValidators()</code> (retrieve all validators)
            </para></listitem>

            <listitem><para>
                <code>removeValidator($name)</code> (remove validator by name)
            </para></listitem>

            <listitem><para>
                <code>clearValidators()</code> (remove all validators)
            </para></listitem>
        </itemizedlist>

        <sect3 id="zend.form.elements.validators.errors">
            <title>Custom Error Messages</title>

            <para>
                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.
            </para>

            <itemizedlist>
                <listitem><para>
                    <code>addErrorMessage($message)</code>: 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.
                </para></listitem>

                <listitem><para>
                    <code>addErrorMessages(array $messages)</code>: add multiple
                    error messages to display on form validation errors.
                </para></listitem>

                <listitem><para>
                    <code>setErrorMessages(array $messages)</code>: add multiple
                    error messages to display on form validation errors,
                    overwriting all previously set error messages.
                </para></listitem>

                <listitem><para>
                    <code>getErrorMessages()</code>: retrieve the list of
                    custom error messages that have been defined.
                </para></listitem>

                <listitem><para>
                    <code>clearErrorMessages()</code>: remove all custom error
                    messages that have been defined.
                </para></listitem>

                <listitem><para>
                    <code>markAsError()</code>: mark the element as having
                    failed validation.
                </para></listitem>

                <listitem><para>
                    <code>hasErrors()</code>: determine whether the element has
                    either failed validation or been marked as invalid.
                </para></listitem>

                <listitem><para>
                    <code>addError($message)</code>: add a message to the custom
                    error messages stack and flag the element as invalid.
                </para></listitem>

                <listitem><para>
                    <code>addErrors(array $messages)</code>: add several
                    messages to the custom error messages stack and flag the
                    element as invalid.
                </para></listitem>

                <listitem><para>
                    <code>setErrors(array $messages)</code>: overwrite the
                    custom error messages stack with the provided messages and
                    flag the element as invalid.
                </para></listitem>
            </itemizedlist>

            <para>
                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.
            </para>
        </sect3>
    </sect2>

    <sect2 id="zend.form.elements.decorators">
        <title>Decorators</title>

        <para>
            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.
        </para>

        <para>
            <classname>Zend_Form_Element</classname> 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 <link
                linkend="zend.form.decorators">Zend_Form_Decorator</link>.
        </para>

        <para>
            The default decorators used by <classname>Zend_Form_Element</classname> are:
        </para>

        <itemizedlist>
            <listitem><para>
                <emphasis>ViewHelper</emphasis>: 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,
                <classname>Zend_Form_Element</classname> specifies the 'formText' view
                helper, but individual subclasses specify different helpers.
            </para></listitem>

            <listitem><para>
                <emphasis>Errors</emphasis>: appends error messages to the
                element using <classname>Zend_View_Helper_FormErrors</classname>. If none are present,
                nothing is appended.
            </para></listitem>

            <listitem><para>
                <emphasis>Description</emphasis>: appends the element
                description. If none is present, nothing is appended. By
                default, the description is rendered in a &lt;p&gt; tag with a
                class of 'description'.
            </para></listitem>

            <listitem><para>
                <emphasis>HtmlTag</emphasis>: wraps the element and errors in
                an HTML &lt;dd&gt; tag.
            </para></listitem>

            <listitem><para>
                <emphasis>Label</emphasis>: prepends a label to the element
                using <classname>Zend_View_Helper_FormLabel</classname>, and wraps it in a &lt;dt&gt;
                tag. If no label is provided, just the definition term tag is
                rendered.
            </para></listitem>
        </itemizedlist>

        <note>
            <title>Default Decorators Do Not Need to Be Loaded</title>

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

            <programlisting role="php"><![CDATA[
$element = new Zend_Form_Element('foo',
                                 array('disableLoadDefaultDecorators' =>
                                      true)
                                );
]]></programlisting>

            <para>
                This option may be mixed with any other options you pass,
                both as array options or in a <classname>Zend_Config</classname> object.
            </para>
        </note>

        <para>
            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:
        </para>

        <programlisting role="php"><![CDATA[
$this->addDecorators(array(
    array('ViewHelper'),
    array('Errors'),
    array('Description', array('tag' => 'p', 'class' => 'description')),
    array('HtmlTag', array('tag' => 'dd')),
    array('Label', array('tag' => 'dt')),
));
]]></programlisting>

        <para>
            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 &lt;dd&gt; tag.
            Finally, the last decorator, 'label', retrieves the element's label
            and passes it to the 'FormLabel' view helper, wrapping it in an HTML
            &lt;dt&gt; tag; the value is prepended to the content by default.
            The resulting output looks basically like this:
        </para>

        <programlisting role="html"><![CDATA[
<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>
]]></programlisting>

        <para>
            For more information on decorators, read the <link
                linkend="zend.form.decorators">Zend_Form_Decorator
                section</link>.
        </para>

        <note>
            <title>Using Multiple Decorators of the Same Type</title>

            <para>
                Internally, <classname>Zend_Form_Element</classname> 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.
            </para>

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

            <programlisting role="php"><![CDATA[
// Alias to 'FooBar':
$element->addDecorator(array('FooBar' => 'HtmlTag'),
                       array('tag' => 'div'));

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

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

            <programlisting role="php"><![CDATA[
// 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');
]]></programlisting>
        </note>

        <para>
            Methods associated with decorators include:
        </para>

        <itemizedlist>
            <listitem><para>
                <code>addDecorator($nameOrDecorator, array $options = null)</code>
            </para></listitem>

            <listitem><para>
                <code>addDecorators(array $decorators)</code>
            </para></listitem>

            <listitem><para>
                <code>setDecorators(array $decorators)</code> (overwrites all decorators)
            </para></listitem>

            <listitem><para>
                <code>getDecorator($name)</code> (retrieve a decorator object by name)
            </para></listitem>

            <listitem><para>
                <code>getDecorators()</code> (retrieve all decorators)
            </para></listitem>

            <listitem><para>
                <code>removeDecorator($name)</code> (remove decorator by name)
            </para></listitem>

            <listitem><para>
                <code>clearDecorators()</code> (remove all decorators)
            </para></listitem>
        </itemizedlist>

        <para>
            <classname>Zend_Form_Element</classname> also uses overloading to allow rendering
            specific decorators. <code>__call()</code> 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
            <emphasis>single</emphasis> decorator. Any arguments passed to the
            method call will be used as content to pass to the decorator's
            <code>render()</code> method. As an example:
        </para>

        <programlisting role="php"><![CDATA[
// 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");
]]></programlisting>

        <para>
            If the decorator does not exist, an exception is raised.
        </para>
    </sect2>

    <sect2 id="zend.form.elements.metadata">
        <title>Metadata and Attributes</title>

        <para>
            <classname>Zend_Form_Element</classname> handles a variety of attributes and
            element metadata. Basic attributes include:
        </para>

        <itemizedlist>
            <listitem><para>
                <emphasis>name</emphasis>: the element name. Uses the
                <code>setName()</code> and <code>getName()</code> accessors.
            </para></listitem>

            <listitem><para>
                <emphasis>label</emphasis>: the element label. Uses the
                <code>setLabel()</code> and <code>getLabel()</code> accessors.
            </para></listitem>

            <listitem><para>
                <emphasis>order</emphasis>: the index at which an element
                should appear in the form. Uses the <code>setOrder()</code> and
                <code>getOrder()</code> accessors.
            </para></listitem>

            <listitem><para>
                <emphasis>value</emphasis>: the current element value. Uses the
                <code>setValue()</code> and <code>getValue()</code> accessors.
            </para></listitem>

            <listitem><para>
                <emphasis>description</emphasis>: a description of the element;
                often used to provide tooltip or javascript contextual hinting
                describing the purpose of the element. Uses the
                <code>setDescription()</code> and <code>getDescription()</code>
                accessors.
            </para></listitem>

            <listitem><para>
                <emphasis>required</emphasis>: flag indicating whether or not
                the element is required when performing form validation. Uses
                the <code>setRequired()</code> and <code>getRequired()</code>
                accessors. This flag is false by default.
            </para></listitem>

            <listitem><para>
                <emphasis>allowEmpty</emphasis>: 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 <code>setAllowEmpty()</code> and <code>getAllowEmpty()</code>
                accessors. This flag is true by default.
            </para></listitem>

            <listitem><para>
                <emphasis>autoInsertNotEmptyValidator</emphasis>: 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 <code>setAutoInsertNotEmptyValidator($flag)</code> and
                determine the value with
                <code>autoInsertNotEmptyValidator()</code>.
            </para></listitem>
        </itemizedlist>

        <para>
            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:
        </para>

        <itemizedlist>
            <listitem><para>
                <emphasis>setAttrib($name, $value)</emphasis>: add an attribute
            </para></listitem>

            <listitem><para>
                <emphasis>setAttribs(array $attribs)</emphasis>: like
                addAttribs(), but overwrites
            </para></listitem>

            <listitem><para>
                <emphasis>getAttrib($name)</emphasis>: retrieve a single
                attribute value
            </para></listitem>

            <listitem><para>
                <emphasis>getAttribs()</emphasis>: retrieve all attributes as
                key/value pairs
            </para></listitem>
        </itemizedlist>

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

        <programlisting role="php"><![CDATA[
// Equivalent to $element->setAttrib('class', 'text'):
$element->class = 'text;
]]></programlisting>

        <para>
            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.
        </para>
    </sect2>

    <sect2 id="zend.form.elements.standard">
        <title>Standard Elements</title>

        <para>
            <classname>Zend_Form</classname> ships with a number of standard elements; please read the
            <link linkend="zend.form.standardElements">Standard Elements</link>
            chapter for full details.
        </para>
    </sect2>

    <sect2 id="zend.form.elements.methods">
        <title>Zend_Form_Element Methods</title>

        <para>
            <classname>Zend_Form_Element</classname> has many, many methods. What follows
            is a quick summary of their signatures, grouped by type:
        </para>

        <itemizedlist>
            <listitem><para>Configuration:</para>
                <itemizedlist>
                    <listitem><para><code>setOptions(array $options)</code></para></listitem>
                    <listitem><para><code>setConfig(Zend_Config $config)</code></para></listitem>
                </itemizedlist>
            </listitem>

            <listitem><para>I18n:</para>
                <itemizedlist>
                    <listitem><para><code>setTranslator(Zend_Translate_Adapter $translator = null)</code></para></listitem>
                    <listitem><para><code>getTranslator()</code></para></listitem>
                    <listitem><para><code>setDisableTranslator($flag)</code></para></listitem>
                    <listitem><para><code>translatorIsDisabled()</code></para></listitem>
                </itemizedlist>
            </listitem>

            <listitem><para>Properties:</para>
                <itemizedlist>
                    <listitem><para><code>setName($name)</code></para></listitem>
                    <listitem><para><code>getName()</code></para></listitem>
                    <listitem><para><code>setValue($value)</code></para></listitem>
                    <listitem><para><code>getValue()</code></para></listitem>
                    <listitem><para><code>getUnfilteredValue()</code></para></listitem>
                    <listitem><para><code>setLabel($label)</code></para></listitem>
                    <listitem><para><code>getLabel()</code></para></listitem>
                    <listitem><para><code>setDescription($description)</code></para></listitem>
                    <listitem><para><code>getDescription()</code></para></listitem>
                    <listitem><para><code>setOrder($order)</code></para></listitem>
                    <listitem><para><code>getOrder()</code></para></listitem>
                    <listitem><para><code>setRequired($flag)</code></para></listitem>
                    <listitem><para><code>getRequired()</code></para></listitem>
                    <listitem><para><code>setAllowEmpty($flag)</code></para></listitem>
                    <listitem><para><code>getAllowEmpty()</code></para></listitem>
                    <listitem><para><code>setAutoInsertNotEmptyValidator($flag)</code></para></listitem>
                    <listitem><para><code>autoInsertNotEmptyValidator()</code></para></listitem>
                    <listitem><para><code>setIgnore($flag)</code></para></listitem>
                    <listitem><para><code>getIgnore()</code></para></listitem>
                    <listitem><para><code>getType()</code></para></listitem>
                    <listitem><para><code>setAttrib($name, $value)</code></para></listitem>
                    <listitem><para><code>setAttribs(array $attribs)</code></para></listitem>
                    <listitem><para><code>getAttrib($name)</code></para></listitem>
                    <listitem><para><code>getAttribs()</code></para></listitem>
                </itemizedlist>
            </listitem>

            <listitem><para>Plugin loaders and paths:</para>
                <itemizedlist>
                    <listitem><para><code>setPluginLoader(Zend_Loader_PluginLoader_Interface $loader, $type)</code></para></listitem>
                    <listitem><para><code>getPluginLoader($type)</code></para></listitem>
                    <listitem><para><code>addPrefixPath($prefix, $path, $type = null)</code></para></listitem>
                    <listitem><para><code>addPrefixPaths(array $spec)</code></para></listitem>
                </itemizedlist>
            </listitem>

            <listitem><para>Validation:</para>
                <itemizedlist>
                    <listitem><para><code>addValidator($validator, $breakChainOnFailure = false, $options = array())</code></para></listitem>
                    <listitem><para><code>addValidators(array $validators)</code></para></listitem>
                    <listitem><para><code>setValidators(array $validators)</code></para></listitem>
                    <listitem><para><code>getValidator($name)</code></para></listitem>
                    <listitem><para><code>getValidators()</code></para></listitem>
                    <listitem><para><code>removeValidator($name)</code></para></listitem>
                    <listitem><para><code>clearValidators()</code></para></listitem>
                    <listitem><para><code>isValid($value, $context = null)</code></para></listitem>
                    <listitem><para><code>getErrors()</code></para></listitem>
                    <listitem><para><code>getMessages()</code></para></listitem>
                </itemizedlist>
            </listitem>

            <listitem><para>Filters:</para>
                <itemizedlist>
                    <listitem><para><code>addFilter($filter, $options = array())</code></para></listitem>
                    <listitem><para><code>addFilters(array $filters)</code></para></listitem>
                    <listitem><para><code>setFilters(array $filters)</code></para></listitem>
                    <listitem><para><code>getFilter($name)</code></para></listitem>
                    <listitem><para><code>getFilters()</code></para></listitem>
                    <listitem><para><code>removeFilter($name)</code></para></listitem>
                    <listitem><para><code>clearFilters()</code></para></listitem>
                </itemizedlist>
            </listitem>

            <listitem><para>Rendering:</para>
                <itemizedlist>
                    <listitem><para><code>setView(Zend_View_Interface $view = null)</code></para></listitem>
                    <listitem><para><code>getView()</code></para></listitem>
                    <listitem><para><code>addDecorator($decorator, $options = null)</code></para></listitem>
                    <listitem><para><code>addDecorators(array $decorators)</code></para></listitem>
                    <listitem><para><code>setDecorators(array $decorators)</code></para></listitem>
                    <listitem><para><code>getDecorator($name)</code></para></listitem>
                    <listitem><para><code>getDecorators()</code></para></listitem>
                    <listitem><para><code>removeDecorator($name)</code></para></listitem>
                    <listitem><para><code>clearDecorators()</code></para></listitem>
                    <listitem><para><code>render(Zend_View_Interface $view = null)</code></para></listitem>
                </itemizedlist>
            </listitem>
        </itemizedlist>
    </sect2>

    <sect2 id="zend.form.elements.config">
        <title>Configuration</title>

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

        <itemizedlist>
            <listitem><para>
                If 'set' + key refers to a <classname>Zend_Form_Element</classname>
                method, then the value provided will be passed to that method.
            </para></listitem>

            <listitem><para>
                Otherwise, the value will be used to set an attribute.
            </para></listitem>
        </itemizedlist>

        <para>
            Exceptions to the rule include the following:
        </para>

        <itemizedlist>
            <listitem><para>
                <code>prefixPath</code> will be passed to
                <code>addPrefixPaths()</code>
            </para></listitem>

            <listitem>
                <para>
                    The following setters cannot be set in this way:
                </para>

                <itemizedlist>
                    <listitem><para>
                            <code>setAttrib</code> (though
                            <code>setAttribs</code> <emphasis>will</emphasis>
                            work)
                    </para></listitem>

                    <listitem><para><code>setConfig</code></para></listitem>

                    <listitem><para><code>setOptions</code></para></listitem>

                    <listitem><para><code>setPluginLoader</code></para></listitem>

                    <listitem><para><code>setTranslator</code></para></listitem>

                    <listitem><para><code>setView</code></para></listitem>
                </itemizedlist>
            </listitem>
        </itemizedlist>

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

        <programlisting role="ini"><![CDATA[
[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"
; 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"
]]></programlisting>
    </sect2>

    <sect2 id="zend.form.elements.custom">
        <title>Custom Elements</title>

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

        <itemizedlist>
            <listitem><para>
                Elements that share common validators and/or filters
            </para></listitem>

            <listitem><para>
                Elements that have custom decorator functionality
            </para></listitem>
        </itemizedlist>

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

        <para>
            As an example, let's say that all text elements in a form you are
            creating need to be filtered with <code>StringTrim</code>,
            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:
        </para>

        <programlisting role="php"><![CDATA[
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');
    }
}
]]></programlisting>

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

        <programlisting role="php"><![CDATA[
$form->addPrefixPath('My_Element', 'My/Element/', 'element')
     ->addElement('text', 'foo');
]]></programlisting>

        <para>
            The 'foo' element will now be of type <code>My_Element_Text</code>,
            and exhibit the behaviour you've outlined.
        </para>

        <para>
            Another method you may want to override when extending
            <classname>Zend_Form_Element</classname> is the
            <code>loadDefaultDecorators()</code> 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:
        </para>

        <programlisting role="php"><![CDATA[
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'));
    }
}
]]></programlisting>

        <para>
            There are many ways to customize elements. Read the API
            documentation of <classname>Zend_Form_Element</classname> to learn about all of the
            available methods.
        </para>
    </sect2>
</sect1>
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