NAME
    Validation::Class - Centralized Input Validation for Any Application

VERSION
    version 2.4.4

SYNOPSIS
        use MyApp::Validation;
        
    my $input = MyApp::Validation->new(params => $params);
        
    unless ($input->validate()){
            return $input->errors_to_string;
        }

DESCRIPTION
    Validation::Class is a different approach to data validation, it
    attempts to simplify and centralize data validation rules to ensure DRY
    (don't repeat yourself) code. The primary intent of this module is to
    provide a simplistic validation framework. Your validation class is your
    data input firewall and can be used anywhere and is flexible enough in
    an MVC environment to be used in both the Controller and Model. A
    validation class is defined as follows:

        package MyApp::Validation;
        
    use Validation::Class;
        
    # a validation rule
        field 'login'  => {
            label      => 'User Login',
            error      => 'Login invalid.',
            required   => 1,
            validation => sub {
                my ($self, $this_field, $all_params) = @_;
                return $this_field->{value} eq 'admin' ? 1 : 0;
            }
        };
        
    # a validation rule
        field 'password'  => {
            label         => 'User Password',
            error         => 'Password invalid.',
            required      => 1,
            validation    => sub {
                my ($self, $this_field, $all_params) = @_;
                return $this_field->{value} eq 'pass' ? 1 : 0;
            }
        };
        
    1;

    The fields defined will be used to validate the specified input
    parameters. You specify the input parameters at instantiaton, parameters
    should take the form of a hashref of key/value pairs. Multi-level
    (nested) hashrefs are allowed and are inflated/deflated in accordance
    with the rules of Hash::Flatten or your hash inflator configuration. The
    following is an example on using your validate class to validate input
    in various scenarios:

        # web app
        package MyApp;
        
    use MyApp::Validation;
        use Misc::WebAppFramework;
        
    get '/auth' => sub {
            # get user input parameters
            my $params = shift;
        
        # initialize validation class and set input parameters
            my $rules = MyApp::Validation->new(params => $params);
            
        unless ($rules->validate('login', 'password')) {
                
            # print errors to browser unless validation is successful
                return $rules->errors_to_string;
            }
            
        return 'you have authenticated';
        };

CHANGE NOTICE
    Important Note! Validation::Class is subject to change, though not
    dramatically, you've been warned. Users of this library pre-v2 should
    not that the error accessors were changed. Validation::Class has been
    re-written using Moose. Sorry if you feel this bloats your application
    but using Moose was the better approach.

BUILDING A VALIDATION CLASS
        package MyApp::Validation;
        
    use Validation::Class;
        
    # a validation rule template
        mixin 'basic'  => {
            required   => 1,
            min_length => 1,
            max_length => 255,
            filters    => ['lowercase', 'alphanumeric']
        };
        
    # a validation rule
        field 'user.login'  => {
            mixin      => 'basic',
            label      => 'user login',
            error      => 'login invalid',
            validation => sub {
                my ($self, $this, $fields) = @_;
                return $this->{value} eq 'admin' ? 1 : 0;
            }
        };
        
    # a validation rule
        field 'user.password'  => {
            mixin         => 'basic',
            label         => 'user login',
            error         => 'login invalid',
            validation    => sub {
                my ($self, $this, $fields) = @_;
                return $this->{value} eq 'pass' ? 1 : 0;
            }
        };
        
    1;

  THE MIXIN KEYWORD
    The mixin keyword creates a validation rules template that can be
    applied to any field using the mixin directive.

        package MyApp::Validation;
        use Validation::Class;
        
    mixin 'constrain' => {
            required   => 1,
            min_length => 1,
            max_length => 255,
            ...
        };
        
    # e.g.
        field 'login' => {
            mixin => 'constrain',
            ...
        };

  THE FILTER KEYWORD
    The filter keyword creates custom filters to be used in your field
    definitions.

        package MyApp::Validation;
        use Validation::Class;
        
    filter 'usa_telephone_number_converter' => sub {
            $_[0] =~ s/\D//g;
            my ($ac, $pre, $num) = $_[0] =~ /(\d{3})(\d{3})(\d{4})/;
            $_[0] = "($ac) $pre-$num";
        };
        
    # e.g.
        field 'my_telephone' => {
            filter => ['trim', 'usa_telephone_number_converter'],
            ...
        };

  THE DIRECTIVE KEYWORD
    The directive keyword creates custom validator directives to be used in
    your field definitions. The routine is passed two parameters, the value
    of directive and the value of the field the validator is being processed
    against. The validator should return true or false.

        package MyApp::Validation;
        use Validation::Class;
        
    directive 'between' => sub {
            my ($directive, $value, $field, $class) = @_;
            my ($min, $max) = split /\-/, $directive;
            unless ($value > $min && $value < $max) {
                my $handle = $field->{label} || $field->{name};
                $class->error($field, "$handle must be between $directive");
                return 0;
            }
            return 1;
        };
        
    # e.g.
        field 'hours' => {
            between => '00-24',
            ...
        };

  THE FIELD KEYWORD
    The field keyword creates a validation block and defines validation
    rules for reuse in code. The field keyword should correspond with the
    parameter name expected to be passed to your validation class.

        package MyApp::Validation;
        use Validation::Class;
        
    field 'login' => {
            required   => 1,
            min_length => 1,
            max_length => 255,
            ...
        };

    The field keword takes two arguments, the field name and a hashref of
    key/values pairs.

AUTO-SERIALIZATION/DESERIALIZATION
    Validation::Class supports hash automatic serialization/deserialization
    which means that you can set the parameters using a hashref of nested
    hashrefs and validate against them, or set the parameters using a
    hashref of key/value pairs and validate against that. This function is
    provided in Validation::Class via Hash::Flatten. The following is an
    example of that:

        my $params = {
            user => {
                login => 'admin',
                password => 'pass'
            }
        };
        
    my $rules = MyApp::Validation->new(params => $params);
        
    # or
        
    my $params = {
            'user.login' => 'admin',
            'user.password' => 'pass'
        };
        
    my $rules = MyApp::Validation->new(params => $params);
        
    # field definition using field('user.login', ...)
        # and field('user.password', ...) will match against the parameters above
        
    # after filtering, validation, etc ... return your params as a hashref if
        # needed
        
    my $params = $rules->get_params_hash;

SEPERATION OF CONCERNS
    For larger applications were a single validation class might become
    cluttered and inefficient Validation::Class come equipped to help you
    seperate your validation rules into seperate classes.

    The idea is that you'll end up with a main validation class (most-likely
    empty) that will simply serve as your point of entry into your relative
    (child) classes. The following is an example of this:

        package MyVal::User;
        use Validation::Class;
        
    field name => { ... };
        field email => { ... };
        field login => { ... };
        field password => { ... };
        
    package MyVal::Profile;
        use Validation::Class;
        
    field age => { ... };
        field sex => { ... };
        field birthday => { ... };
        
    package MyVal;
        use Validation::Class;
        
    __PACKAGE__->load_classes;
        
    package main;
        
    my $rules = MyVal->new(params => $params);
        my $user = $rules->class('user');
        my $profile = $rules->class('profile');
        
    ...
        
    1;

DEFAULT FIELD/MIXIN DIRECTIVES
        package MyApp::Validation;
        use Validation::Class;
        
    # a validation template
        mixin '...'  => {
            # mixin directives here
            ...
        };
        
    # a validation rule
        field '...'  => {
            # field directives here
            ...
        };
        
    1;

    When building a validation class, the first encountered and arguably two
    most important keyword functions are field() and mixin() which are used
    to declare their respective properties. A mixin() declares a validation
    template where its properties are intended to be copied within field()
    declarations which declares validation rules, filters and other
    properties.

    Both the field() and mixin() declarations/functions require two
    parameters, the first being a name, used to identify the declaration and
    to be matched against incoming input parameters, and the second being a
    hashref of key/value pairs. The key(s) within a declaration are commonly
    referred to as directives.

    The following is a list of default directives which can be used in
    field/mixin declarations:

  alias
    The alias directive is useful when many different parameters with
    different names can be validated using a single rule. E.g. The paging
    parameters in a webapp may take on different names but require the same
    validation.

        # the alias directive
        field 'pager'  => {
            alias => ['page_user_list', 'page_other_list']
            ...
        };

  default
    The default directive is used as a default value for a field to be used
    when a matching parameter is not present.

        # the default directive
        field 'quantity'  => {
            default => 1,
            ...
        };

  error/errors
    The error/errors directive is used to replace the system generated error
    messages when a particular field doesn't validate. If a field fails
    multiple directives, multiple errors will be generate for the same
    field. This may not be desirable, the error directive overrides this
    behavior and only the specified error is registered and displayed.

        # the error(s) directive
        field 'foobar'  => {
            errors => 'Foobar failed processing, Wtf?',
            ...
        };

  label
    The label directive is used as a user-friendly reference when the field
    name is a serialized hash key or just plain ugly.

        # the label directive
        field 'hashref.foo.bar'  => {
            label => 'Foo Bar',
            ...
        };

  mixin
    The mixin directive is used to create a template of directives to be
    applied to other fields.

        mixin 'ID' => {
            required => 1,
            min_length => 1,
            max_length => 11
        };

        # the mixin directive
        field 'user.id'  => {
            mixin => 'ID',
            ...
        };

  mixin_field
    The mixin directive is used to copy all directives from an existing
    field except for the name, label, and validation directives.

        # the mixin_field directive
        field 'foobar'  => {
            label => 'Foo Bar',
            required => 1
        };
        
    field 'barbaz'  => {
            mixin_field => 'foobar',
            label => 'Bar Baz',
            ...
        };

  name
    The name directive is used *internally* and cannot be changed.

        # the name directive
        field 'thename'  => {
            ...
        };

  required
    The required directive is an important directive but can be
    misunderstood. The required directive used to ensure the *submitted*
    parameter exists and has a value. If the parameter is never submitted,
    the required directive has no effect and *in-fact* all filtering,
    validation, etc is then skipped.

        # the required directive
        field 'foobar'  => {
            required => 1,
            ...
        };
        
    # fail
        my $rules = MyApp::Validation->new(params => {  });
        $rules->validate('foobar');
        
    # pass
        my $rules = MyApp::Validation->new(params => {  foobar => 'Nii=cce });
        $rules->validate('foobar');

    See the toggle functionality within the validate() method. This method
    allows you to temporarily alter whether a field is required or not.

  validation
    The validation directive is a coderef used add additional custom
    validation to the field.

        # the validation directive
        field 'login'  => {
            validation => sub {
                my ($self, $this_field, $all_params) = @_;
                return 0 unless $this_field->{value};
                return $this_field->{value} eq 'admin' ? 1 : 0;
            },
            ...
        };

  value
    The value directive is used internally to store the field's matching
    parameter's value. This value can be set in the definition but SHOULD
    NOT be used as a default value unless you're sure no parameter will
    overwrite it during runtime. If you need to set a default value, see the
    default directive.

        # the value directive
        field 'quantity'  => {
            value => 1,
            ...
        };

DEFAULT FIELD/MIXIN FILTER DIRECTIVES
  filter/filters
    The filter/filters directive is used to correct, altering and/or format
    the values of the matching input parameter. Note: Filtering is applied
    before validation. The filter directive can have multiple filters (even
    a coderef) in the form of an arrayref of values.

        # the filter(s) directive
        field 'text'  => {
            filter => [qw/trim strip/ => sub {
                $_[0] =~ s/\D//g;
            }],
            ...
        };

    The following is a list of default filters that may be used with the
    filter directive:

   alpha
    The alpha filter removes all non-Alphabetic characters from the field's
    value.

        field 'foobar'  => {
            filter => 'alpha',
        };

   alphanumeric
    The alpha filter removes all non-Alphabetic and non-Numeric characters
    from the field's value.

        field 'foobar'  => {
            filter => 'alphanumeric',
        };

   capitalize
    The capitalize filter attempts to capitalize the first word in each
    sentence, where sentences are seperated by a period and space, within
    the field's value.

        field 'foobar'  => {
            filter => 'capitalize',
        };

   decimal
    The decimal filter removes all non-decimal-based characters from the
    field's value. Allows-only: decimal, comma, and numbers.

        field 'foobar'  => {
            filter => 'decimal',
        };

   numeric
    The numeric filter removes all non-Numeric characters from the field's
    value.

        field 'foobar'  => {
            filter => 'numeric',
        };

   strip
    As with the trim filter the strip filter removes leading and trailing
    whitespaces from the field's value and additionally removes multiple
    whitespaces from between the values characters.

        field 'foobar'  => {
            filter => 'strip',
        };

   titlecase
    The titlecase filter converts the field's value to titlecase by
    capitalizing the first letter of each word.

        field 'foobar'  => {
            filter => 'titlecase',
        };

   trim
    The trim filter removes leading and trailing whitespaces from the
    field's value.

        field 'foobar'  => {
            filter => 'trim',
        };

   uppercase
    The uppercase filter converts the field's value to uppercase.

        field 'foobar'  => {
            filter => 'uppercase',
        };

DEFAULT FIELD/MIXIN VALIDATOR DIRECTIVES
        package MyApp::Validation;
        
    use Validation::Class;
        
    # a validation rule with validator directives
        field 'telephone_number'  => {
            length => 14,
            pattern => '(###) ###-####',
            ...
        };
        
    1;

    Validator directives are special directives with associated validation
    code that is used to validate common use-cases such as "checking the
    length of a parameter", etc.

    The following is a list of the default validators which can be used in
    field/mixin declarations:

  between
        # the between directive
        field 'foobar'  => {
            between => '1-5',
            ...
        };

  depends_on
        # the depends_on directive
        field 'change_password'  => {
            depends_on => ['password', 'password_confirm'],
            ...
        };

  length
        # the length directive
        field 'foobar'  => {
            length => 20,
            ...
        };

  matches
        # the matches directive
        field 'this_field'  => {
            matches => 'another_field',
            ...
        };

  max_alpha
        # the max_alpha directive
        field 'password'  => {
            max_alpha => 30,
            ...
        };

  max_digits
        # the max_digits directive
        field 'password'  => {
            max_digits => 5,
            ...
        };

  max_length
        # the max_length directive
        field 'foobar'  => {
            max_length => '...',
            ...
        };

  max_sum
        # the max_sum directive
        field 'vacation_days'  => {
            max_sum => 5,
            ...
        };

  max_symbols
        # the max_symbols directive
        field 'password'  => {
            max_symbols => 1,
            ...
        };

  min_alpha
        # the min_alpha directive
        field 'password'  => {
            min_alpha => 2,
            ...
        };

  min_digits
        # the min_digits directive
        field 'password'  => {
            min_digits => 1,
            ...
        };

  min_length
        # the min_length directive
        field 'foobar'  => {
            min_length => '...',
            ...
        };

  min_sum
        # the min_sum directive
        field 'vacation_days'  => {
            min_sum => 0,
            ...
        };

  min_symbols
        # the min_symbols directive
        field 'password'  => {
            min_symbols => 0,
            ...
        };

  options
        # the options directive
        field 'status'  => {
            options => 'Active, Inactive',
            ...
        };

  pattern
        # the pattern directive
        field 'telephone'  => {
            pattern => '### ###-####',
            ...
        };
        
    field 'country_code'  => {
            pattern => 'XX',
            filter  => 'uppercase'
            ...
        };

THE VALIDATION CLASS
    The following is an example of how to use your constructed validation
    class in other code, .e.g. Web App Controller, etc.

        use MyApp::Validation;
        
    my $input = MyApp::Validation->new(params => $params);
        unless ($input->validate('field1','field2')){
            return $input->errors_to_string;
        }

    Feeling lazy, have your validation class automatically find the
    appropriate fields to validate against (params must match field names).

        use MyApp::Validation;
        
    my $input = MyApp::Validation->new(params => $params);
        unless ($input->validate){
            return $input->errors_to_string;
        }

    You can define an alias to automatically map a parameter to a validation
    field whereby a field definition will have an alias attribute containing
    an arrayref of alternate parameters that can be matched against
    passed-in parameters.

        package MyApp::Validation;
        
    field 'foo.bar' => {
            ...,
            alias => [
                'foo',
                'bar',
                'baz',
                'bax'
            ]
        };

        use MyApp::Validation;
        
    my  $input = MyApp::Validation->new(params => { foo => 1 });
        unless ($input->validate(){
            return $input->errors_to_string;
        }

  new
    The new method instantiates and returns an instance of your validation
    class.

        use MyApp::Validation;
        
    my $input = MyApp::Validation->new;
        $input->params($params);
        ...
        
    my $input = MyApp::Validation->new(params => $params);
        ...

VALIDATION CLASS ATTRIBUTES
  ignore_unknown
    The ignore_unknown boolean determines whether your application will live
    or die upon encountering unregistered field directives during
    validation.

        my $self = MyApp::Validation->new(params => $params, ignore_unknown => 1);
        $self->ignore_unknown(1);
        ...

  fields
    The fields attribute returns a hashref of defined fields, filtered and
    merged with thier parameter counterparts.

        my $self = MyApp::Validation->new(fields => $fields);
        my $fields = $self->fields();
        ...

  filters
    The filters attribute returns a hashref of pre-defined filter
    definitions.

        my $filters = $self->filters();
        ...

  hash_inflator
    The hash_inflator value determines how the hash serializer
    (inflation/deflation) behaves. The value must be a hashref of "OPTIONS"
    in Hash::Flatten options. Purely for the sake of consistency, you can
    use lowercase keys (with underscores) which will be converted to
    camelcased keys before passed to the serializer.

        my $self = MyApp::Validation->new(
            hash_inflator => {
                hash_delimiter => '/',
                array_delimiter => '//'
            }
        );
        ...

  mixins
    The mixins attribute returns a hashref of defined validation templates.

        my $mixins = $self->mixins();
        ...

  params
    The params attribute gets/sets the parameters to be validated.

        my $input = {
            ...
        };
        
    my $self = MyApp::Validation->new(params => $input);
        
    $self->params($input);
        my $params = $self->params();
        
    ...

  report_unknown
    The report_unknown boolean determines whether your application will
    report unregistered fields as class-level errors upon encountering
    unregistered field directives during validation.

        my $self = MyApp::Validation->new(params => $params,
        ignore_unknown => 1, report_unknown => 1);
        $self->report_unknown(1);
        ...

  reset_fields
    The reset_fields attribute effectively resets any altered field objects
    at the class level. This method is called automatically everytime the
    new() method is triggered.

        $self->reset_fields();

  stashed
    The stashed attribute represents a list of field names stored to be used
    in validation later. If the stashed attribute contains a list you can
    omit arguments to the validate method.

        $self->stashed([qw/this that .../]);

VALIDATION CLASS METHODS
  class
    The class method returns a new initialize child validation class under
    the namespace of the calling class that issued the load_classes() method
    call. Existing parameters and configuration options are passed to the
    child class's constructor. All attributes can be easily overwritten
    using the attribute's accessors on the child class.

        package MyVal;
        use Validation::Class; __PACKAGE__->load_classes;
        
    package main;
        
    my $rules = MyVal->new(params => $params);
        
    my $kid1 = $rules->class('child'); # loads MyVal::Child;
        my $kid2 = $rules->class('step_child'); # loads MyVal::StepChild;
        
    1;

  error
    The error function is used to set and/or retrieve errors encountered
    during validation. The error function with no parameters returns the
    error message object which is an arrayref of error messages stored at
    class-level.

        # return all errors encountered/set as an arrayref
        return $self->error();
        
    # return all errors specific to the specified field (at the field-level)
        # as an arrayref
        return $self->error('some_param');
        
    # set an error specific to the specified field (at the field-level)
        # using the field object (hashref not field name)
        $self->error($field_object, "i am your error message");

        unless ($self->validate) {
            my $fields = $self->error();
        }

  error_count
    The error_count function returns the total number of error encountered
    from the last validation call.

        return $self->error_count();
        
    unless ($self->validate) {
            print "Found ". $self->error_count ." Errors";
        }

  error_fields
    The error_fields method returns a hashref of fields whose value is an
    arrayref of error messages.

        unless ($self->validate) {
            my $bad_fields = $self->error_fields();
        }

  errors_to_string
    The errors_to_string function stringifies the error arrayref object
    using the specified delimiter or ', ' by default.

        return $self->errors_to_string();
        return $self->errors_to_string("<br/>\n");
        
    unless ($self->validate) {
            return $self->errors_to_string;
        }

  get_params
    The get_params method returns the values (in list form) of the
    parameters specified.

        if ($self->validate) {
            my $name_a = $self->get_params('name');
            my ($name_b, $email, $login, $password) =
                $self->get_params(qw/name email login password/);
            
        # you should note that if the params dont exist they will return undef
            # ... meaning you should check that it exists before checking its value
            # e.g.
            
        if (defined $name) {
                if ($name eq '') {
                    print 'name parameter was passed but was empty';
                }
            }
            else {
                print 'name parameter was never submitted';
            }
        }

  get_params_hash
    If your fields and parameters are designed with complex hash structures,
    The get_params_hash method returns the deserialized hashref of specified
    parameters based on the the default or custom configuration of the hash
    serializer Hash::Flatten.

        my $params = {
            'user.login' => 'member',
            'user.password' => 'abc123456'
        };
        
    if ($self->validate(keys %$params)) {
            my $params = $self->get_params_hash;
            print $params->{user}->{login};
        }

  load_classes
    The load_classes method is used Module::Find to load child classes for
    convenient access through the class() method. Existing parameters and
    configuration options are passed to the child class's constructor. All
    attributes can be easily overwritten using the attribute's accessors on
    the child class.

        package MyVal;
        use Validation::Class; __PACKAGE__->load_classes;
        1;

  load_plugins
    The load_plugins method is used to load plugins that support
    Validation::Class. A Validation::Class plugin is little more than a Role
    (Moose::Role) that extends the Validation::Class core. As usual, an
    official Validation::Class plugin can be referred to using shorthand
    while custom plugins are called by prefixing a plus symbol to the
    fully-qualified plugin name. Learn more about plugins at
    Validation::Class::Plugins.

        package MyVal;
        use Validation::Class;
        
    __PACKAGE__->load_plugins('SuperX');
        # loads Validation::Class::Plugin::SuperX
        
    __PACKAGE__->load_plugins('+MyApp::Validation::Plugin::SuperY');
        
    1;

  param
    The param method returns a single parameter by name.

        if ($self->param('chng_pass')) {
            $self->validate('password_confirmation');
        }

  queue
    The queue method is a convenience method used specifically to append the
    stashed attribute allowing you to *queue* field to be validated. This
    method also allows you to set fields that must always be validated.

        # conditional validation flow WITHOUT the queue method
        # imagine a user profile update action
        
    my $rules = MyApp::Validation->new(params => $params);
        my @fields = qw/name login/;
        
    push @fields, 'email_confirm' if $rules->param('chg_email');
        push @fields, 'password_confirm' if $rules->param('chg_pass');
        
    ... if $rules->validate(@fields);
        
    # conditional validation WITH the queue method
        
    my $rules = MyApp::Validation->new(params => $params);
        
    $rules->queue(qw/name login/);
        $rules->queue(qw/email_confirm/) if $rules->param('chg_email');
        $rules->queue(qw/password_confirm/) if $rules->param('chg_pass');
        
    ... if $rules->validate();
        
    # set fields that must ALWAYS be validated
        # imagine a simple REST server
        
    my $rules = MyApp::Validation->new(params => $params);
        
    $rules->queue(qw/login password/);
        
    if ($request eq '/resource/:id') {
            
        if ($rules->validate('id')) {
                
            # validated login, password and id
                ...
            }
        }

  set_params_hash
    Depending on how parameters are being input into your application, if
    your input parameters are already complex hash structures, The
    set_params_hash method will set and return the serialized version of
    your hashref based on the the default or custom configuration of the
    hash serializer Hash::Flatten.

        my $params = {
            user => {
                login => 'member',
                password => 'abc123456'
            }
        };
        
    my $serialized_params = $self->set_params_hash($params);

  reset
    The reset method clears all errors, fields and stashed field names, both
    at the class and individual field levels.

        $self->reset();

  reset_errors
    The reset_errors method clears all errors, both at the class and
    individual field levels. This method is called automatically everytime
    the validate() method is triggered.

        $self->reset_errors();

  reset_fields
    The reset_fields method clears all errors and field values, both at the
    class and individual field levels. This method is called automatically
    everytime the validate() method is triggered.

        $self->reset_fields();

  validate
    The validate method returns true/false depending on whether all
    specified fields passed validation checks.

        use MyApp::Validation;
        
    my $input = MyApp::Validation->new(params => $params);
        
    # validate specific fields
        unless ($input->validate('field1','field2')){
            return $input->errors_to_string;
        }
        
    # validate existing parameters, if no parameters exist,
        # validate all fields ... which will return true unless field(s) exist
        # with a required directive
        unless ($input->validate()){
            return $input->errors_to_string;
        }
        
    # validate all fields period, obviously
        unless ($input->validate(keys %{$input->fields})){
            return $input->errors_to_string;
        }
        
    # validate specific parameters (by name) after mapping them to other fields
        my $parameter_map = {
            user => 'hey_im_not_named_login',
            pass => 'password_is_that_really_you'
        };
        unless ($input->validate($parameter_map)){
            return $input->errors_to_string;
        }

    Another cool trick the validate() method can perform is the ability to
    temporarily alter whether a field is required or not during runtime.
    This functionality is often referred to as the *toggle* function.

    This function is important when you define a field (or two or three) as
    required or non and want to change that per validation. This is done by
    calling the validate() method with a list of fields to be validated and
    prefixing the target fields with a plus or minus as follows:

        use MyApp::Validation;
        
    my $input = MyApp::Validation->new(params => $params);
        
    # validate specific fields, force name, email and phone to be required
        # regardless of the field definitions directives ... and force the age, sex
        # and birthday to be optional
        
    my @spec = qw(+name +email +phone -age -sex -birthday);
        
    unless ($input->validate(@spec)){
            return $input->errors_to_string;
        }

AUTHOR
    Al Newkirk <awncorp@cpan.org>

COPYRIGHT AND LICENSE
    This software is copyright (c) 2011 by awncorp.

    This is free software; you can redistribute it and/or modify it under
    the same terms as the Perl 5 programming language system itself.