def read_attribute(name)
      name = name.to_s
      value = @attributes[name]
      accessed(name, value)
    end
def read_attribute(name)
      name = name.to_s
      value = @attributes[name]
      accessed(name, value)
    end
TODO: Add typecasting
 Read a value from the +Document+ attributes. If the value does not exist
 it will return nil.