Validates that the value of a field is within a range/set.

This validation is defined by passing a field along with a :set parameter. The :set can be a Range or any object which responds to the include? method (an array, for example).

@example Usage

  require 'dm-validations'

  class Review
    include DataMapper::Resource

    STATES = ['new', 'in_progress', 'published', 'archived']

    property :title, String
    property :body, String
    property :review_state, String
    property :rating, Integer

    validates_within :review_state, :set => STATES
    validates_within :rating,       :set => 1..5

    # a call to valid? will return false unless
    # the two properties conform to their sets
  end