Validates whether the value of the specified xml attribute/element has a valid email format.

Example:

  <contact email="mail@xample.com">...</contact>

  class Contact < Adaptation::Message
    has_one :attribute, :email

    validates_as_email :email
  end

Validates whether the value of the specified xml attribute/element is the expected one.

Example 1:

  <leftwing side="left"/>

  class Leftwing < Adaptation::Message
    has_one :attribute, :side

    validates_value_of :side, "left"
  end

Example 2:

  <bird><wings><wing side="left"/><wing side="right"/></wings></bird>

  class Bird < Adaptation::Message
    has_many :wings

    validates_value_of :side, "left", :in => :wings
  end