# File lib/rubygems/specification.rb, line 474
  def self.from_yaml(input)
    input = normalize_yaml_input input
    spec = YAML.load input

    if spec && spec.class == FalseClass then
      raise Gem::EndOfYAMLException
    end

    unless Gem::Specification === spec then
      raise Gem::Exception, "YAML data doesn't evaluate to gem specification"
    end

    unless (spec.instance_variables.include? '@specification_version' or
            spec.instance_variables.include? :@specification_version) and
           spec.instance_variable_get :@specification_version
      spec.instance_variable_set :@specification_version,
                                 NONEXISTENT_SPECIFICATION_VERSION
    end

    spec
  end