类 Psych::AnchorNotDefined

为了向后兼容性，继承了 ‘BadAlias`

公共类方法

new(anchor_name) 点击切换源代码
调用超类方法 
# File psych/lib/psych/exception.rb, line 18
def initialize anchor_name
  super "An alias referenced an unknown anchor: #{anchor_name}"
end